Wayland: Fix error paths not closing sending fd

Whatever error happens on our end, we should still close the fd so the
other end can move on.

(cherry picked from commit 990dc4b388)

README.md

@@ -133,6 +133,7 @@ information on what to include when reporting a bug.
    `glfwGetClipboardString`
  - [Wayland] Bugfix: Data source creation error would cause double free at termination
  - [Wayland] Bugfix: Partial writes of clipboard string would cause beginning to repeat
+ - [Wayland] Bugfix: Some errors would cause clipboard string transfer to hang
 
 
 ## Contact

src/wl_window.c

@@ -1733,6 +1733,7 @@ static void dataSourceHandleSend(void* userData,
     {
         _glfwInputError(GLFW_PLATFORM_ERROR,
                         "Wayland: Unknown clipboard data source");
+        close(fd);
         return;
     }
 
@@ -1740,6 +1741,7 @@ static void dataSourceHandleSend(void* userData,
     {
         _glfwInputError(GLFW_PLATFORM_ERROR,
                         "Wayland: Copy requested from an invalid string");
+        close(fd);
         return;
     }