Win32 Register .webm extension

(cherry picked from commit 9c1e5242ab9bf554524e175fa8e546b8d01cba4f)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

extras/package/win32/vlc.win32.nsi.in

@@ -271,6 +271,7 @@ FunctionEnd
   !insertmacro ${_action} ".ts"
   !insertmacro ${_action} ".vob"
   !insertmacro ${_action} ".vro"
+  !insertmacro ${_action} ".webm"
   !insertmacro ${_action} ".wmv"
 !macroend