Fix docs and remove redundant C code

docs/reST/ref/surface.rst

@@ -326,7 +326,10 @@
       Scrolling is contained by the Surface clip area. It is safe to have dx
       and dy values that exceed the surface size.
 
-      The scroll flag can be ``0`` (normal behavior) or:
+      The scroll flag can be:
+         * ``0`` (default): the pixels are shifted but previous pixels are
+           not modified.
+
          * ``pygame.SCROLL_ERASE``: the space created by the shifting pixels
            is filled with black or transparency.
 

src_c/surface.c

@@ -2529,9 +2529,7 @@ surf_scroll(PyObject *self, PyObject *args, PyObject *keywds)
     }
 
     if (scroll(surf, dx, dy, x, y, w, h, repeat, erase) < 0) {
-        if (!pgSurface_Unlock((pgSurfaceObject *)self)) {
-            return NULL;
-        }
+        pgSurface_Unlock((pgSurfaceObject *)self);
         return NULL;
     }