Further limit max input size in parser fuzzer

It's easy to cause stack overflows with degenerate cases like
"$$$$$x" repeated thousands of times. We have no interest in
addressing these.

Make the input size smaller to hopefully avoid these stack
overflows.

Author: nikic

sapi/fuzzer/fuzzer-parser.c

@@ -26,8 +26,8 @@
 #include "fuzzer-sapi.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
-	if (Size > 32 * 1024) {
-		/* Large inputs have a large impact on fuzzer performance,
+	if (Size > 7 * 1024) {
+		/* Large inputs have a large impact on fuzzer performance and may cause stack overflows,
 		 * but are unlikely to be necessary to reach new codepaths. */
 		return 0;
 	}

sapi/fuzzer/generate_parser_corpus.php

@@ -9,7 +9,7 @@
 $corpusDir = __DIR__ . '/corpus/parser';
 @mkdir($corpusDir);
 
-$maxLen = 32 * 1024;
+$maxLen = 7 * 1024;
 foreach ($it as $file) {
     if (!preg_match('/\.phpt$/', $file)) continue;
     $code = file_get_contents($file);