don't crash page when gs goes caster's up.
just let the 0-pages code kick in and exit
gracefully.

Reference: /n/sources/patch/applied/pagenopages
Date: Thu Apr 28 17:54:57 CES 2011
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/page/pdf.c	Thu Apr 28 17:54:52 2011
+++ /sys/src/cmd/page/pdf.c	Thu Apr 28 17:54:51 2011
@@ -106,8 +106,10 @@
 	setdim(pdf, Rect(0,0,0,0), ppi, 0);
 	gscmd(pdf, "(%s) (r) file { DELAYSAFER { .setsafe } if } stopped pop pdfopen begin\n", fn);
 	gscmd(pdf, "pdfpagecount PAGE==\n");
-	p = Brdline(&pdf->gsrd, '\n');
-	npage = atoi(p);
+	
+	npage = 0;
+	if(p = Brdline(&pdf->gsrd, '\n'))
+		npage = atoi(p);
 	if(npage < 1) {
 		fprint(2, "no pages?\n");
 		return nil;