reset clipping path when the state is restored

According to the specification, see NOTE 2 in

it appears that the clipping path should be reset
when the restore (Q) operator is encountered.

Fixes #739
diff --git a/poppler/ b/poppler/
index f1c69b7..2db12d8 100644
--- a/poppler/
+++ b/poppler/
@@ -5380,6 +5380,7 @@
     state = state->restore();
+    clip = clipNone;
 // Create a new state stack, and initialize it with a copy of the