Don't run off the end of a string.

Fixes #7461

common/common.cpp

@@ -169,8 +169,16 @@ wxString KIwxExpandEnvVars( const wxString& str, const PROJECT* aProject )
             size_t m = n + 1;
             wxUniChar str_m = str[m];
 
-            while( m < strlen && ( wxIsalnum( str_m ) || str_m == wxT( '_' ) || str_m == wxT( ':' ) ) )
-                str_m = str[++m];
+            while( wxIsalnum( str_m ) || str_m == wxT( '_' ) || str_m == wxT( ':' ) )
+            {
+                if( ++m == strlen )
+                {
+                    str_m = 0;
+                    break;
+                }
+
+                str_m = str[m];
+            }
 
             wxString strVarName( str.c_str() + n + 1, m - n - 1 );