Bug 1629006

Description of problem:
Isolated to the "Calculator" tab, all other tabs seem to work perfectly.

When the user hits 'enter' after typing an expression in the entry field, the view above it does not show a rendering of previously entered expressions or the associated answers.

Version-Release number of selected component (if applicable):
kalgebra-18.04.3-1.fc28.x86_64
qt5-qtwebengine-5.11.1-4.fc28.x86_64

How reproducible:
100%

Steps to Reproduce:
1. open kalgebra
2. type "1+1"
3. hit enter

Actual results:
* The expression is highlighted, ready to be replaced by over-typing.
* The variables pane on the right is updated, showing the answer in 'ans', and adding any variables you may have assigned.

Expected results:
* The expression and answer should appear above the entry field, in addition to the actual results.

Additional info:
* only tested on two x11 setups
* seems to happen on both kde & gnome environments
* right-clicking in the area that the history tape is expected produces a *DISJOINT* "Clear" menu that is outside of the window entirely (not even near the mouse)... furthermore activating that 'clear' option produces the below stacktrace.

Diagnostic output:
Received signal 11 SEGV_MAPERR ffffffffffffffff
#0 0x7f76cecdea2e <unknown>
#1 0x7f76cecdeb40 <unknown>
#2 0x7f76cecdf177 <unknown>
#3 0x7f76c8e71f30 <unknown>
#4 0x55b723256641 <unknown>
#5 0x55b72325bde5 <unknown>
#6 0x7f76c9db6e1e QMetaObject::activate()
#7 0x7f76ca680c26 QAction::triggered()
#8 0x7f76ca6832f0 QAction::activate()
#9 0x7f76ca7f847c <unknown>
#10 0x7f76ca7ffb24 <unknown>
#11 0x7f76ca800b6b QMenu::mouseReleaseEvent()
#12 0x7f76ca6c65c8 QWidget::event()
#13 0x7f76ca80321b QMenu::event()
#14 0x7f76ca687475 QApplicationPrivate::notify_helper()
#15 0x7f76ca68edd8 QApplication::notify()
#16 0x7f76c9d8ec36 QCoreApplication::notifyInternal2()
#17 0x7f76ca68e0cd QApplicationPrivate::sendMouseEvent()
#18 0x7f76ca6e1723 <unknown>
#19 0x7f76ca6e3f0e <unknown>
#20 0x7f76ca687475 QApplicationPrivate::notify_helper()
#21 0x7f76ca68eb90 QApplication::notify()
#22 0x7f76c9d8ec36 QCoreApplication::notifyInternal2()
#23 0x7f76ca134f43 QGuiApplicationPrivate::processMouseEvent()
#24 0x7f76ca137085 QGuiApplicationPrivate::processWindowSystemEvent()
#25 0x7f76ca11246b QWindowSystemInterface::sendWindowSystemEvents()
#26 0x7f76b9f727cf <unknown>
#27 0x7f76c9d8db7b QEventLoop::exec()
#28 0x7f76ca7fd6f4 QMenu::exec()
#29 0x55b723256e71 <unknown>
#30 0x7f76d4570f19 <unknown>
#31 0x7f76cd78cfaa <unknown>
#32 0x7f76ce23a5de <unknown>
#33 0x7f76cdf768c8 <unknown>
#34 0x7f76cdf7fbd6 <unknown>
#35 0x7f76cdf8fb05 <unknown>
#36 0x7f76ce12d51e <unknown>
#37 0x7f76cf591ce4 <unknown>
#38 0x7f76cecdf4d8 <unknown>
#39 0x7f76cecffd3a <unknown>
#40 0x7f76ced007ef <unknown>
#41 0x7f76ced0096a <unknown>
#42 0x7f76cd72682e <unknown>
#43 0x7f76c9db7adb QObject::event()
#44 0x7f76ca687475 QApplicationPrivate::notify_helper()
#45 0x7f76ca68eb90 QApplication::notify()
#46 0x7f76c9d8ec36 QCoreApplication::notifyInternal2()
#47 0x7f76c9d91e0b QCoreApplicationPrivate::sendPostedEvents()
#48 0x7f76c9ddf507 <unknown>
#49 0x7f76c6a0c8ad g_main_context_dispatch
#50 0x7f76c6a0cc78 <unknown>
#51 0x7f76c6a0cd10 g_main_context_iteration
#52 0x7f76c9ddf293 QEventDispatcherGlib::processEvents()
#53 0x7f76b9f727c5 <unknown>
#54 0x7f76c9d8db7b QEventLoop::exec()
#55 0x7f76c9d95c46 QCoreApplication::exec()
#56 0x55b72324a42b <unknown>
#57 0x7f76c8e5e11b __libc_start_main
#58 0x55b72324a4aa _start
  r8: 000055b729ead430  r9: 0000000000000010 r10: 000055b724c48010 r11: 00007f76b0011fb0
 r12: 0000000000000034 r13: 00007ffdd25fc758 r14: 00007ffdd25fc760 r15: 000055b7250e0f10
  di: 0000000000000010  si: 0000000000000000  bp: 00007ffdd25fc900  bx: 000055b729eecfd8
  dx: 000055b729ead430  ax: ffffffffffffffff  cx: 0000000000000001  sp: 00007ffdd25fc730
  ip: 000055b723256641 efl: 0000000000010246 cgf: 002b000000000033 erf: 0000000000000005
 trp: 000000000000000e msk: 0000000000000000 cr2: ffffffffffffffff
[end of stack trace]
Calling _exit(1). Core file will not be generated.