Provide better error message when memoryview data cannot be converted to object

Cython/Compiler/ExprNodes.py

@@ -2548,7 +2548,6 @@ class IndexNode(ExprNode):
                         warning(index.pos, "Index should be typed for more "
                                            "efficient access", level=2)
                         IndexNode.warned_untyped_idx = True
-                elif index.type.is_int:
                     self.memslice_index = True
                     index = index.coerce_to(index_type, env)
                     indices[i] = index

Cython/Utility/MemoryView.pyx

@@ -341,11 +341,14 @@ cdef class memoryview(object):
         cdef bytes bytesitem
         # Do a manual and complete check here instead of this easy hack
         bytesitem = itemp[:self.view.itemsize]
-        result = struct.unpack(self.view.format, bytesitem)
-        if len(self.view.format) == 1:
-            return result[0]
-
-        return result
+        try:
+            result = struct.unpack(self.view.format, bytesitem)
+        except struct.error:
+            raise ValueError("Unable to convert item to object")
+        else:
+            if len(self.view.format) == 1:
+                return result[0]
+            return result
 
     cdef assign_item_from_object(self, char *itemp, object value):
         """Only used if instantiated manually by the user, or if Cython doesn't