[PATCH 1 of 5 stable cpychecker] diffhelpers: verify hline was created before using it

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1422371224 18000
#      Tue Jan 27 10:07:04 2015 -0500
# Branch stable
# Node ID 25af70176080cd54761b1624c900dc19252c9994
# Parent  0c4419faacbcca691737b5e25820dcbf4c7150ac
diffhelpers: verify hline was created before using it

Found with cpychecker.

diff --git a/mercurial/diffhelpers.c b/mercurial/diffhelpers.c
--- a/mercurial/diffhelpers.c
+++ b/mercurial/diffhelpers.c
@@ -34,6 +34,9 @@ static void _fix_newline(PyObject *hunk,
 		sz -= 1;
 
 	hline = PyBytes_FromStringAndSize(l, sz-1);
+	if (!hline) {
+		return NULL;
+	}
 
 	if (c == ' ' || c == '+') {
 		PyObject *rline = PyBytes_FromStringAndSize(l + 1, sz - 2);
@@ -194,4 +197,3 @@ initdiffhelpers(void)
 	                                        NULL, NULL);
 }
 #endif
-