patch 7.4.1282

Problem:    Crash when evaluating the pattern of ":catch" causes an error.
            (Dominique Pelle)
Solution:   Block error messages at this point.

src/ex_eval.c

@@ -1562,7 +1562,11 @@ ex_catch(exarg_T *eap)
 		}
 		save_cpo  = p_cpo;
 		p_cpo = (char_u *)"";
+		/* Disable error messages, it will make current_exception
+		 * invalid. */
+		++emsg_off;
 		regmatch.regprog = vim_regcomp(pat, RE_MAGIC + RE_STRING);
+		--emsg_off;
 		regmatch.rm_ic = FALSE;
 		if (end != NULL)
 		    *end = save_char;