sh: Properly restore exception handler in fc.

If SIGINT arrived at exactly the right moment (unlikely), an exception
handler in a no longer active stack frame would be called.

Because the old handler was not used in the normal path, clang thought it
was a dead value and if an exception happened it would longjmp() to garbage.
This caused builtins/fc1.0 to fail if histedit.c was compiled with clang.

MFC after:	1 week

bin/sh/histedit.c

@@ -232,6 +232,7 @@ histcmd(int argc, char **argv)
 		}
 	argc -= optind, argv += optind;
 
+	savehandler = handler;
 	/*
 	 * If executing...
 	 */
@@ -242,7 +243,6 @@ histcmd(int argc, char **argv)
 		 * Catch interrupts to reset active counter and
 		 * cleanup temp files.
 		 */
-		savehandler = handler;
 		if (setjmp(jmploc.loc)) {
 			active = 0;
 			if (editfile)
@@ -399,6 +399,7 @@ histcmd(int argc, char **argv)
 		--active;
 	if (displayhist)
 		displayhist = 0;
+	handler = savehandler;
 	return 0;
 }