Perform region checking only for region related scan reports.

This bug became noticable after cb122392

, in that we routinely
send a new scan report type, which should not affect region
tracking.

Investigating this revealed that this code was also buggy
in that the region code could cause non region related
scan reports to be discarded.  The code was refactored
to avoid that case.
Acked-by: Frediano Ziglio <fziglio@redhat.com>

src/scan.c

@@ -428,42 +428,52 @@ int scanner_destroy(scanner_t *scanner)
 
 int scanner_push(scanner_t *scanner, scan_type_t type, int x, int y, int w, int h)
 {
-    int rc = X11SPICE_ERR_MALLOC;
-    scan_report_t *r = malloc(sizeof(*r));
-
-    if (r) {
-        r->type = type;
-        r->x = x;
-        r->y = y;
-        r->w = w;
-        r->h = h;
-
-        g_mutex_lock(scanner->lock);
-        if (scanner->queue) {
-            pixman_box16_t rect;
-            rect.x1 = x;
-            rect.x2 = x + w;
-            rect.y1 = y;
-            rect.y2 = y + h;
-
-            if (!pixman_region_contains_rectangle(&scanner->region, &rect)) {
-                pixman_region_union_rect(&scanner->region, &scanner->region, x, y, w, h);
-
-                g_async_queue_push(scanner->queue, r);
-            } else {
-                free(r);
-            }
-            rc = 0;
-        } else {
-            free(r);
-            rc = X11SPICE_ERR_SHUTTING_DOWN;
-        }
-        g_mutex_unlock(scanner->lock);
-    }
+    scan_report_t *r;
+
 #if defined(DEBUG_SCANLINES)
     fprintf(stderr, "scan: type %d, %dx%d @ %dx%d\n", type, w, h, x, y);
     fflush(stderr);
 #endif
 
-    return rc;
+    g_mutex_lock(scanner->lock);
+
+    if (!scanner->queue) {
+        g_mutex_unlock(scanner->lock);
+        return X11SPICE_ERR_SHUTTING_DOWN;
+    }
+
+    r = malloc(sizeof(*r));
+    if (!r) {
+        g_mutex_unlock(scanner->lock);
+        return X11SPICE_ERR_MALLOC;
+    }
+
+    r->type = type;
+    r->x = x;
+    r->y = y;
+    r->w = w;
+    r->h = h;
+
+    if (type == SCANLINE_SCAN_REPORT || type == DAMAGE_SCAN_REPORT) {
+        pixman_box16_t rect;
+        rect.x1 = x;
+        rect.x2 = x + w;
+        rect.y1 = y;
+        rect.y2 = y + h;
+
+        /* Optimization: if we're being notified of an area already to be
+           rescanned, just discard this notice, otherwise update region and push */
+        if (pixman_region_contains_rectangle(&scanner->region, &rect)) {
+            free(r);
+        } else {
+            pixman_region_union_rect(&scanner->region, &scanner->region, x, y, w, h);
+            g_async_queue_push(scanner->queue, r);
+        }
+    } else {
+        g_async_queue_push(scanner->queue, r);
+    }
+
+    g_mutex_unlock(scanner->lock);
+
+    return 0;
 }