Move variable declaration to the top of the block,

to let _json.c compile with Microsoft compilers.

Modules/_json.c

@@ -256,10 +256,11 @@ scanstring_str(PyObject *pystr, Py_ssize_t end, char *encoding, int strict)
         }
         /* Pick up this chunk if it's not zero length */
         if (next != end) {
+            PyObject *strchunk;
             if (PyBuffer_FillInfo(&info, &buf[end], next - end, 1, 0) < 0) {
                 goto bail;
             }
-            PyObject *strchunk = PyMemoryView_FromMemory(&info);
+            strchunk = PyMemoryView_FromMemory(&info);
             if (strchunk == NULL) {
                 goto bail;
             }