fix updater crash due to optimization

Issue:I7I9X5
Test:libc-test, benchmark
Signed-off-by: Nrobottoy <wangyaofeng.wang@huawei.com>
Change-Id: I55f79a8bec9dc890121ec4fea10c982328c2073e
Signed-off-by: Nrobottoy <wangyaofeng.wang@huawei.com>

porting/linux/user/src/stdio/fgets.c

@@ -2,7 +2,6 @@
 #include <string.h>
 
 #define MIN(a,b) ((a)<(b) ? (a) : (b))
-
 char *fgets(char *restrict s, int n, FILE *restrict f)
 {
 	char *p = s;
@@ -15,42 +14,35 @@ char *fgets(char *restrict s, int n, FILE *restrict f)
 	if (n--<=1) {
 		f->mode |= f->mode-1;
 		FUNLOCK(f);
-		if (n) {
-			return NULL;
-		}
-		*s = '\0';
+		if (n) return 0;
+		*s = 0;
 		return s;
 	}
 
 	while (n) {
-		if (f->rpos == f->rend && __fill_buffer(f)) {
-			if (p == s || !feof(f)) {
-				s = 0;
-			}
-			break;
+		if (f->rpos != f->rend) {
+			z = memchr(f->rpos, '\n', MIN(f->rend - f->rpos, n));
+			k = z ? z - f->rpos + 1 : f->rend - f->rpos;
+			k = MIN(k, n);
+			memcpy(p, f->rpos, k);
+			f->rpos += k;
+			p += k;
+			n -= k;
+			if (z || !n) break;
 		}
-
-		/* search minimal length */
-		k = MIN(f->rend - f->rpos, n);
-		z = memchr(f->rpos, '\n', k);
-		if (z != NULL) {
-			k = z - f->rpos + 1;
-		}
-		memcpy(p, f->rpos, k);
-		f->rpos += k;
-		p += k;
-		n -= k;
-		if (z || !n) {
+		if ((c = getc_unlocked(f)) < 0) {
+			if (p==s || !feof(f)) s = 0;
 			break;
 		}
+		n--;
+		if ((*p++ = c) == '\n') break;
 	}
-	if (s) {
-		*p = 0;
-	}
+	if (s) *p = 0;
 
 	FUNLOCK(f);
 
 	return s;
 }
 
+
 weak_alias(fgets, fgets_unlocked);