Fixed HIDAPI hotplug detection in applications that don't initialize video

(cherry picked from commit eaeca340f3828aa706e2cff05bafb61e9132c7f7)

src/SDL.c

@@ -280,6 +280,11 @@ bool SDL_IsMainThread(void)
     return true;
 }
 
+bool SDL_IsVideoThread(void)
+{
+    return (SDL_GetCurrentThreadID() == SDL_VideoThreadID);
+}
+
 // Initialize all the subsystems that require initialization before threads start
 void SDL_InitMainThread(void)
 {

src/SDL_internal.h

@@ -306,6 +306,9 @@ extern SDL_NORETURN void SDL_ExitProcess(int exitcode);
 // Do any initialization that needs to happen before threads are started
 extern void SDL_InitMainThread(void);
 
+// Return true if this thread has initialized video
+extern bool SDL_IsVideoThread(void);
+
 /* The internal implementations of these functions have up to nanosecond precision.
    We can expose these functions as part of the API if we want to later.
 */

src/hidapi/SDL_hidapi.c

@@ -388,7 +388,7 @@ static void HIDAPI_UpdateDiscovery(void)
     }
 
 #if defined(SDL_PLATFORM_WIN32) || defined(SDL_PLATFORM_WINGDK)
-    if (SDL_IsMainThread()) {
+    if (SDL_IsVideoThread()) {
         // just let the usual SDL_PumpEvents loop dispatch these, fixing bug 2998. --ryan.
     } else {
         // We'll only get messages on the same thread that created the window