Only avoid glow context switching on Windows (#4296)

…since it is reportedly broken on Windows

* Early-out added in #4284
* Re-opens #4173 😭 
* Closes #4289
* Closes #4290

crates/eframe/src/native/glow_integration.rs

@@ -849,10 +849,17 @@ fn change_gl_context(
 ) {
     crate::profile_function!();
 
-    if let Some(current_gl_context) = current_gl_context {
-        crate::profile_scope!("is_current");
-        if gl_surface.is_current(current_gl_context) {
-            return; // Early-out to save a lot of time.
+    if !cfg!(target_os = "windows") {
+        // According to https://github.com/emilk/egui/issues/4289
+        // we cannot do this early-out on Windows.
+        // TODO(emilk): optimize context switching on Windows too.
+        // See https://github.com/emilk/egui/issues/4173
+
+        if let Some(current_gl_context) = current_gl_context {
+            crate::profile_scope!("is_current");
+            if gl_surface.is_current(current_gl_context) {
+                return; // Early-out to save a lot of time.
+            }
         }
     }