Fix Str.__getitem__

string.pxd

@@ -43,14 +43,12 @@ cdef cypclass Str "Cy_Str":
 
     char __getitem__(self, int index) except 0:
         cdef int end = self._str.size()
-        cdef int idx = index
         if index < 0:
-            index = -index
-            idx = end - index
-        if index >= end:
-            with gil:
-                raise ValueError('index out of range')
-        return self._str[idx]
+            index = end + index
+        if 0 <= index < end:
+            return self._str[index]
+        with gil:
+            raise ValueError('index out of range')
 
     int find(self, Str s, size_t start=0, size_t stop=0):
         if start < stop and stop <= self._str.size():