* extension.c (eval_ext_lang_from_control_command): Avoid dereferencing
	NULL pointer.

	testsuite/
	* gdb.python/python.exp (python not supported): Verify multi-line
	python command issues an error.
	* gdb.guile/guile.exp (guile not supported): Verify multi-line
	guile command issues an error.
Fix typo in previous entry.