Handle patches with misformatted empty lines

Insert a space on empty lines which are missing a control character.

Signed-off-by: Hollis Blanchard <[e-mail]>
---
I frequently receive emailed patches with empty lines represented as "\n\n",
where Mercurial expects them to be "\n \n". patch(1) applies these patches
without complaint, but qpush fails all hunks.

mercurial/diffhelpers.c

@@ -83,6 +83,12 b' addlines(PyObject *self, PyObject *args)'
 				_fix_newline(hunk, a, b);
 				continue;
 			}
+			if (c == '\n') {
+				/* Some patches may be missing the control char
+				 * on empty lines. Supply a leading space. */
+				Py_DECREF(x);
+				x = PyString_FromString(" \n");
+			}
 			PyList_Append(hunk, x);
 			if (c == '+') {
 				l = PyString_FromString(s + 1);