Wayland: Fix memory leaks in data offer reading

The buffer storing the contents of the data offer being read could leak
if buffer reallocation or reading from the pipe failed.

src/wl_window.c

@@ -1333,6 +1333,7 @@ static char* readDataOfferAsString(struct wl_data_offer* offer, const char* mime
             if (!longer)
             {
                 _glfwInputError(GLFW_OUT_OF_MEMORY, NULL);
+                _glfw_free(string);
                 close(fds[0]);
                 return NULL;
             }
@@ -1352,6 +1353,7 @@ static char* readDataOfferAsString(struct wl_data_offer* offer, const char* mime
             _glfwInputError(GLFW_PLATFORM_ERROR,
                             "Wayland: Failed to read from data offer pipe: %s",
                             strerror(errno));
+            _glfw_free(string);
             close(fds[0]);
             return NULL;
         }