Fix leak of display mode

Author: dreampiggy

SDWebImage/Core/SDWebImageDownloader.m

@@ -26,7 +26,7 @@
 BOOL SDWebImageDownloaderOperationGetCompleted(id<SDWebImageDownloaderOperation> operation) {
     NSCParameterAssert(operation);
     NSNumber *value = objc_getAssociatedObject(operation, SDWebImageDownloaderOperationKey);
-    if (value) {
+    if (value != nil) {
         return value.boolValue;
     } else {
         return NO;

SDWebImage/Private/SDDisplayLink.m

@@ -116,9 +116,14 @@ - (NSTimeInterval)duration {
         // Supports Pro display 120Hz
         CGDirectDisplayID display = CVDisplayLinkGetCurrentCGDisplay(_displayLink);
         CGDisplayModeRef mode = CGDisplayCopyDisplayMode(display);
-        double refreshRate = CGDisplayModeGetRefreshRate(mode);
-        if (refreshRate > 0) {
-            duration = 1.0 / refreshRate;
+        if (mode) {
+            double refreshRate = CGDisplayModeGetRefreshRate(mode);
+            if (refreshRate > 0) {
+                duration = 1.0 / refreshRate;
+            } else {
+                duration = kSDDisplayLinkInterval;
+            }
+            CGDisplayModeRelease(mode);
         } else {
             duration = kSDDisplayLinkInterval;
         }