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.

README.md

@@ -314,6 +314,7 @@ 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
  - [POSIX] Removed use of deprecated function `gettimeofday`
  - [POSIX] Bugfix: `CLOCK_MONOTONIC` was not correctly tested for or enabled
  - [WGL] Disabled the DWM swap interval hack for Windows 8 and later (#1072)

src/wl_window.c

@@ -1599,6 +1599,7 @@ static void dataSourceHandleSend(void* userData,
     {
         _glfwInputError(GLFW_PLATFORM_ERROR,
                         "Wayland: Unknown clipboard data source");
+        close(fd);
         return;
     }
 
@@ -1606,6 +1607,7 @@ static void dataSourceHandleSend(void* userData,
     {
         _glfwInputError(GLFW_PLATFORM_ERROR,
                         "Wayland: Copy requested from an invalid string");
+        close(fd);
         return;
     }