Re: "Key binding failed?!--More--"; Strcat to an empty character buffer, causing garbage

This is intended to resolve GitHub Issue #1650, which I was unable to directly reproduce
on my test system.

This fix assumes that the reported issue was related to cmdstr[BUFSZ] buffer not
getting initialized, thus containing random memory values.

src/cmd.c

@@ -2355,6 +2355,7 @@ handler_rebind_keys_add(boolean keyfirst)
         struct Cmd_bind *prevcmd;
         char cmdstr[BUFSZ];
 
+        cmdstr[0] = '\0';
         i = picks->item.a_int;
         free((genericptr_t) picks);