fix: ignore empty mmproj path arguments

Prevent adding the `--mmproj` flag when the provided path string is empty.
An empty `mmproj_path` previously caused an empty argument to be passed to the model loader, potentially leading to errors or undefined behavior. By filtering out empty strings before pushing the flag, the command line construction is now robust against malformed input.

Author: qnixsynapse

src-tauri/plugins/tauri-plugin-llamacpp/src/args.rs

@@ -147,7 +147,7 @@ impl ArgumentBuilder {
     }
 
     fn add_mmproj_args(&mut self, mmproj_path: Option<String>) {
-        if let Some(path) = mmproj_path {
+        if let Some(path) = mmproj_path.filter(|p| !p.is_empty()) {
             self.args.push("--mmproj".to_string());
             self.args.push(path);
         }