Cocoa: Fix potential leak of CFNumber object

Spotted by Clang static analysis.

README.md

@@ -170,6 +170,8 @@ information on what to include when reporting a bug.
    would abort (#1649)
  - [Cocoa] Bugfix: Non-BMP Unicode codepoint input was reported as UTF-16
    (#1635)
+ - [Cocoa] Bugfix: Failing to retrieve the refresh rate of built-in displays
+   could leak memory
  - [X11] Bugfix: The CMake files did not check for the XInput headers (#1480)
  - [X11] Bugfix: Key names were not updated when the keyboard layout changed
    (#1462,#1528)

src/cocoa_monitor.m

@@ -277,14 +277,20 @@ static double getFallbackRefreshRate(CGDirectDisplayID displayID)
                                             CFSTR("IOFBCurrentPixelCount"),
                                             kCFAllocatorDefault,
                                             kNilOptions);
-        if (!clockRef || !countRef)
-            break;
 
         uint32_t clock = 0, count = 0;
-        CFNumberGetValue(clockRef, kCFNumberIntType, &clock);
-        CFNumberGetValue(countRef, kCFNumberIntType, &count);
-        CFRelease(clockRef);
-        CFRelease(countRef);
+
+        if (clockRef)
+        {
+            CFNumberGetValue(clockRef, kCFNumberIntType, &clock);
+            CFRelease(clockRef);
+        }
+
+        if (countRef)
+        {
+            CFNumberGetValue(countRef, kCFNumberIntType, &count);
+            CFRelease(countRef);
+        }
 
         if (clock > 0 && count > 0)
             refreshRate = clock / (double) count;