grep: fix --fixed-strings combined with expression.

"git grep --fixed-strings -e GIT --and -e VERSION .gitignore"
misbehaved because we did not notice this needs to grab lines
that have the given two fixed strings at the same time.

Signed-off-by: Junio C Hamano <junkio@cox.net>

grep.c

@@ -138,15 +138,12 @@ void compile_grep_patterns(struct grep_opt *opt)
 {
 	struct grep_pat *p;
 
-	if (opt->fixed)
-		return;
-
-	/* First compile regexps */
 	for (p = opt->pattern_list; p; p = p->next) {
 		switch (p->token) {
 		case GREP_PATTERN: /* atom */
 		case GREP_PATTERN_HEAD:
 		case GREP_PATTERN_BODY:
+			if (!opt->fixed)
 				compile_regexp(p, opt);
 			break;
 		default: