Fix error reported by ASAN in 139.asan.0.581.pdf

==15244== ERROR: AddressSanitizer: SEGV on unknown address 0x605df000f3ee (pc 0x7f1087b3a22e sp 0x7fffec30ff20 bp 0x7fffec30ff80 T0)
AddressSanitizer can not provide additional info.
    #0 0x7f1087b3a22d (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x48f22d)
    #1 0x7f1087b19d92 (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x46ed92)
    #2 0x7f1087ae570b (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x43a70b)
    #3 0x7f1087ae4061 (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x439061)
    #4 0x7f1087ab9b38 (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x40eb38)
    #5 0x7f1087900989 (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x255989)
    #6 0x7f10878f733a (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x24c33a)
    #7 0x7f10878f650f (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x24b50f)
    #8 0x7f10878f6163 (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x24b163)
    #9 0x7f10879d8dd1 (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x32ddd1)
    #10 0x7f10879e02fd (/home/tsdgeos/devel/poppler/build-debug/libpoppler.so.46.0.0+0x3352fd)
    #11 0x40311e (/home/tsdgeos/devel/poppler/build-debug/utils/pdftoppm+0x40311e)
    #12 0x404416 (/home/tsdgeos/devel/poppler/build-debug/utils/pdftoppm+0x404416)
    #13 0x7f1087000ec4 (/lib/x86_64-linux-gnu/libc-2.19.so+0x21ec4)
    #14 0x401d58 (/home/tsdgeos/devel/poppler/build-debug/utils/pdftoppm+0x401d58)

splash/SplashXPathScanner.cc

@@ -11,7 +11,7 @@
 // All changes made under the Poppler project to this file are licensed
 // under GPL version 2 or later
 //
-// Copyright (C) 2008, 2010 Albert Astals Cid <[email protected]>
+// Copyright (C) 2008, 2010, 2014 Albert Astals Cid <[email protected]>
 // Copyright (C) 2010 Paweł Wiejacha <[email protected]>
 // Copyright (C) 2013 Thomas Freitag <[email protected]>
 //
@@ -514,7 +514,7 @@ void SplashXPathScanner::clipAALine(SplashBitmap *aaBuf,
     xx0 = (*x1 + 1) * splashAASize;
     if (xx0 > aaBuf->getWidth()) xx0 = aaBuf->getWidth();
     // set [xx, xx0) to 0
-    if (xx < xx0) {
+    if (xx < xx0 && xx >= 0) {
       p = aaBuf->getDataPtr() + yy * aaBuf->getRowSize() + (xx >> 3);
       if (xx & 7) {
 	mask = (Guchar)(0xff00 >> (xx & 7));