Fix memory leak on portable builds

The function get_server_path() sometimes returned an owned string,
sometimes a non-owned string.

Always return an allocated (owned) string, and free it after usage.

app/src/server.c

@@ -18,20 +18,31 @@
 #define DEFAULT_SERVER_PATH PREFIX "/share/scrcpy/" SERVER_FILENAME
 #define DEVICE_SERVER_PATH "/data/local/tmp/scrcpy-server.jar"
 
-static const char *
+static char *
 get_server_path(void) {
     const char *server_path_env = getenv("SCRCPY_SERVER_PATH");
     if (server_path_env) {
-        LOGD("Using SCRCPY_SERVER_PATH: %s", server_path_env);
         // if the envvar is set, use it
-        return server_path_env;
+        char *server_path = SDL_strdup(server_path_env);
+        if (!server_path) {
+            LOGE("Could not allocate memory");
+            return NULL;
+        }
+        LOGD("Using SCRCPY_SERVER_PATH: %s", server_path);
+        return server_path;
     }
 
 #ifndef PORTABLE
     LOGD("Using server: " DEFAULT_SERVER_PATH);
+    char *server_path = SDL_strdup(DEFAULT_SERVER_PATH);
+    if (!server_path) {
+        LOGE("Could not allocate memory");
+        return NULL;
+    }
     // the absolute path is hardcoded
-    return DEFAULT_SERVER_PATH;
+    return server_path;
 #else
+
     // use scrcpy-server in the same directory as the executable
     char *executable_path = get_executable_path();
     if (!executable_path) {
@@ -67,12 +78,17 @@ get_server_path(void) {
 
 static bool
 push_server(const char *serial) {
-    const char *server_path = get_server_path();
+    char *server_path = get_server_path();
+    if (!server_path) {
+        return false;
+    }
     if (!is_regular_file(server_path)) {
         LOGE("'%s' does not exist or is not a regular file\n", server_path);
+        SDL_free(server_path);
         return false;
     }
     process_t process = adb_push(serial, server_path, DEVICE_SERVER_PATH);
+    SDL_free(server_path);
     return process_check_success(process, "adb push");
 }