Avoid computer arithmetics with null pointer.

git-svn-id: https://svn.r-project.org/R/trunk@87508 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: kalibera

src/gnuwin32/dos_wglob.c

@@ -598,7 +598,8 @@ glob0(const wchar_t *pattern, wglob_t *pglob)
 	pglob->gl_flags = oldflags;
 	return(globextend(qpat, pglob, &limit));
     }
-    else if (!(pglob->gl_flags & GLOB_NOSORT))
+    else if (!(pglob->gl_flags & GLOB_NOSORT) &&
+	      (pglob->gl_pathc - oldpathc) > 0)
 	qsort(pglob->gl_pathv + pglob->gl_offs + oldpathc,
 	      pglob->gl_pathc - oldpathc, sizeof(wchar_t *),
 	      (pglob->gl_flags & (GLOB_ALPHASORT|GLOB_NOCASE))