Fix unnecessary Ollama model loading (#35032)

Closes https://github.com/zed-industries/zed/issues/35031

Similar solution as in https://github.com/zed-industries/zed/pull/30589

Release Notes:

- Fix unnecessary ollama model loading

crates/language_models/src/provider/ollama.rs

@@ -192,12 +192,16 @@ impl LanguageModelProvider for OllamaLanguageModelProvider {
         IconName::AiOllama
     }
 
-    fn default_model(&self, cx: &App) -> Option<Arc<dyn LanguageModel>> {
-        self.provided_models(cx).into_iter().next()
+    fn default_model(&self, _: &App) -> Option<Arc<dyn LanguageModel>> {
+        // We shouldn't try to select default model, because it might lead to a load call for an unloaded model.
+        // In a constrained environment where user might not have enough resources it'll be a bad UX to select something
+        // to load by default.
+        None
     }
 
-    fn default_fast_model(&self, cx: &App) -> Option<Arc<dyn LanguageModel>> {
-        self.default_model(cx)
+    fn default_fast_model(&self, _: &App) -> Option<Arc<dyn LanguageModel>> {
+        // See explanation for default_model.
+        None
     }
 
     fn provided_models(&self, cx: &App) -> Vec<Arc<dyn LanguageModel>> {