[fuzz] Don't fail when blob is empty

And enable more tests able to trig the issue.

test/fuzzing/hb-subset-fuzzer.cc

@@ -42,7 +42,7 @@ trySubset (hb_face_t *face,
     unsigned int bytes_count = 0;
     for (unsigned int i = 0; i < length; ++i)
       if (data[i]) ++bytes_count;
-    assert (bytes_count);
+    assert (bytes_count || !length);
 
     hb_blob_destroy (blob);
   }

test/fuzzing/run-subset-fuzzer-tests.py

@@ -33,7 +33,7 @@ def cmd(command):
 		def timeout(p, is_killed):
 			is_killed['value'] = True
 			p.kill()
-		timer = threading.Timer (2, timeout, [p, is_killed])
+		timer = threading.Timer (5, timeout, [p, is_killed])
 
 		try:
 			timer.start()
@@ -82,6 +82,8 @@ def run_dir (parent_path):
 	global fails
 	for file in os.listdir (parent_path):
 		path = os.path.join(parent_path, file)
+		# TODO: Run on all the fonts not just subset related ones
+		if "subset" not in path: continue
 
 		print ("running subset fuzzer against %s" % path)
 		if valgrind:
@@ -91,7 +93,7 @@ def run_dir (parent_path):
 			if 'error' in text:
 				returncode = 1
 
-		if not valgrind and text.strip ():
+		if (not valgrind or returncode) and text.strip ():
 			print (text)
 
 		if returncode != 0:
@@ -100,8 +102,7 @@ def run_dir (parent_path):
 
 
 run_dir (os.path.join (srcdir, "..", "subset", "data", "fonts"))
-# TODO running these tests very slow tests.  Fix and re-enable
-#run_dir (os.path.join (srcdir, "fonts"))
+run_dir (os.path.join (srcdir, "fonts"))
 
 if fails:
         print ("%i subset fuzzer related tests failed." % fails)