libsegment: fix for all-in-memory cache

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@73516 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/segment/flush.c

@@ -33,9 +33,11 @@ int Segment_flush(SEGMENT * SEG)
 {
     int i;
 
-    for (i = 0; i < SEG->nseg; i++)
-	if (SEG->scb[i].n >= 0 && SEG->scb[i].dirty)
-	    seg_pageout(SEG, i);
+    if (SEG->scb) {
+	for (i = 0; i < SEG->nseg; i++)
+	    if (SEG->scb[i].n >= 0 && SEG->scb[i].dirty)
+		seg_pageout(SEG, i);
+    }
 
     return 0;
 }