Fix CVE-2007-2721 (heap corruption in jpc_qcx_getcompparms()).

Copied from Fedora.

http://pkgs.fedoraproject.org/cgit/rpms/jasper.git/tree/patch-libjasper-stepsizes-overflow.diff

--- jasper-1.900.1.orig/src/libjasper/jpc/jpc_cs.c	2007-01-19 22:43:07.000000000 +0100
+++ jasper-1.900.1/src/libjasper/jpc/jpc_cs.c	2007-04-06 01:29:02.000000000 +0200
@@ -982,7 +982,10 @@ static int jpc_qcx_getcompparms(jpc_qcxc
 		compparms->numstepsizes = (len - n) / 2;
 		break;
 	}
-	if (compparms->numstepsizes > 0) {
+	if (compparms->numstepsizes > 3 * JPC_MAXRLVLS + 1) {
+		jpc_qcx_destroycompparms(compparms);
+                return -1;
+        } else if (compparms->numstepsizes > 0) {
 		compparms->stepsizes = jas_malloc(compparms->numstepsizes *
 		  sizeof(uint_fast16_t));
 		assert(compparms->stepsizes);