changed count to return 0 for slices outside the source string

Lib/test/string_tests.py

@@ -115,7 +115,8 @@ class CommonTest(unittest.TestCase):
         self.checkequal(2, 'aaa', 'count', 'a', 0, -1)
         self.checkequal(0, 'aaa', 'count', 'a', 0, -10)
         self.checkequal(3, 'aaa', 'count', '', 1)
-        self.checkequal(1, 'aaa', 'count', '', 10)
+        self.checkequal(1, 'aaa', 'count', '', 3)
+        self.checkequal(0, 'aaa', 'count', '', 10)
         self.checkequal(2, 'aaa', 'count', '', -1)
         self.checkequal(4, 'aaa', 'count', '', -10)
 

Objects/stringlib/count.h

@@ -15,7 +15,7 @@ stringlib_count(const STRINGLIB_CHAR* str, Py_ssize_t str_len,
 
     if (sub_len == 0) {
         if (str_len < 0)
-            return 1; /* start >= len(str) */
+            return 0; /* start > len(str) */
         return str_len + 1;
     }