Description of problem: 
bash -c 'TZ=UTC0 :' causes segfault

The RHS can be any value, not just UTC0.

Version-Release number of selected component (if applicable): x86_64 0:4.2.5-1.fc15


How reproducible: always


Steps to Reproduce:
1. bash -c 'TZ=x :'
2.
3.
  
Actual results: 

$ bash -c 'TZ=x :'
zsh: segmentation fault  bash -c 'TZ=UTC0 :'

Expected results:

no segfault

Additional info:

This bug was introduced with patch bash42-005:
This function must accommodate v == NULL, since exported_p dereferences its argument.  Patch attached.

+ int
+ chkexport (name)
+      char *name;
+ {
+   SHELL_VAR *v;
+ 
+   v = find_variable (name);
+   if (exported_p (v))
+     {
+       array_needs_making = 1;
+       maybe_make_export_env ();
+       return 1;
+     }
+   return 0;
+ }