Fix crash when setting invalid label with "&" at the end.

We detected that the label was invalid and gave a debug warning message about
it but then still proceeded to crash by accessing the data beyond the end of
the string. Don't do this.

Closes #15665.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75179 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -570,6 +570,15 @@ Major new features in this release
   was added.
 
 
+
+3.0.1: (released 2014-xx-xx)
+----------------------------
+
+All (GUI):
+
+- Fix crash when setting invalid label ending with "&" (ZaneUJi).
+
+
 3.0.0: (released 2013-11-11)
 ----------------------------