Fixed crash retrieving the name of some displays.

README.md

@@ -55,6 +55,7 @@ guide in the GLFW documentation.
  - [Cocoa] Bugfix: Full screen windows were never reported as having focus
  - [Cocoa] Bugfix: A superfluous I/O flag test prevented video modes from being
                    listed for Thunderbolt monitor
+ - [Cocoa] Bugfix: Retrieving the name of some external displays caused segfault
  - [X11] Added setting of the `WM_CLASS` property to the initial window title
  - [X11] Bugfix: Removed joystick axis value negation left over from GLFW 2
  - [X11] Bugfix: The position of hidden windows was ignored by Metacity

src/cocoa_monitor.m

@@ -49,9 +49,11 @@ static const char* getDisplayName(CGDirectDisplayID displayID)
                                          kIODisplayOnlyPreferredName);
     names = CFDictionaryGetValue(info, CFSTR(kDisplayProductName));
 
-    if (!CFDictionaryGetValueIfPresent(names, CFSTR("en_US"),
+    if (!names || !CFDictionaryGetValueIfPresent(names, CFSTR("en_US"),
                                                  (const void**) &value))
     {
+        _glfwInputError(GLFW_PLATFORM_ERROR, "Failed to retrieve display name");
+
         CFRelease(info);
         return strdup("Unknown");
     }