GLResolver: fall back to app-managed EGL/GLES when a user resolver is set

On platforms where the current GL context cannot be probed via the
platform's native APIs (e.g. ANGLE on tvOS/iOS, where the app owns an
EGL context backed by Metal and there is no system EGL/GLX/WGL to
query), GLResolver::Initialize() failed hard even though the embedding
application had explicitly supplied a resolver via
projectm_create_with_opengl_load_proc().

When a user resolver is present, the app has taken responsibility for
providing GL entry points, so an unprobeable context is expected rather
than an error: assume an app-managed EGL/GLES context and continue,
logging at info level. Behaviour without a user resolver is unchanged
(hard error as before).

Author: keeper-of-memes

src/libprojectM/Renderer/Platform/GLResolver.cpp

@@ -404,9 +404,20 @@ auto GLResolver::Initialize(UserResolver resolver, void* userData) -> bool
         std::string reason;
         if (!HasCurrentContext(currentContext, reason))
         {
-            m_loaded = false;
-            LOG_ERROR(std::string("[GLResolver] No current GL context present: ") + reason);
-            return false;
+            if (state.m_userResolver != nullptr)
+            {
+                currentContext.eglCurrent = true;
+                currentContext.eglAvailable = true;
+                LOG_INFO(std::string("[GLResolver] Current context could not be probed: ") +
+                         reason +
+                         "; assuming app-managed EGL/GLES context because a user resolver was supplied");
+            }
+            else
+            {
+                m_loaded = false;
+                LOG_ERROR(std::string("[GLResolver] No current GL context present: ") + reason);
+                return false;
+            }
         }
     }