warn instead of exiting when it is not possible to get version from git

internal/core/versiongetter/main.go

@@ -69,8 +69,7 @@ func gitDescribeTags(repo *git.Repository) (string, error) {
 	}
 }
 
-func do() error {
-	log.Println("getting mediamtx version...")
+func tagFromGit() error {
 
 	// [git.PlainOpen] uses a ChrootOS that limits filesystem access to the .git directory only.
 	//
@@ -115,6 +114,21 @@ func do() error {
 	return nil
 }
 
+func do() error {
+	log.Println("getting mediamtx version...")
+
+	err := tagFromGit()
+	if err != nil {
+		log.Println("WARN: cannot get tag from .git folder, using v0.0.0 as version")
+		err = os.WriteFile("VERSION", []byte("v0.0.0"), 0o644)
+		if err != nil {
+			return fmt.Errorf("failed to write version file: %w", err)
+		}
+	}
+
+	return nil
+}
+
 func main() {
 	err := do()
 	if err != nil {