Avoid crashes for invalid value of key modifiers

* src/keyboard.c (parse_solitary_modifier): If the argument SYMBOL
is not a symbol, don't try to recognize it.  See
http://lists.gnu.org/archive/html/emacs-devel/2016-08/msg00502.html
for the details.

* test/src/keymap-tests.el (keymap-where-is-internal-test): New
test, for testing the above fix.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/keyboard.c b/src/keyboard.c
index f27ca0f86e0..e44155260f8 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -6621,7 +6621,12 @@ has the same base event type and all the specified modifiers.  */)
 int
 parse_solitary_modifier (Lisp_Object symbol)
 {
-  Lisp_Object name = SYMBOL_NAME (symbol);
+  Lisp_Object name;
+
+  if (!SYMBOLP (symbol))
+    return 0;
+
+  name = SYMBOL_NAME (symbol);
 
   switch (SREF (name, 0))
     {