Recognize the new .webm extension in interfaces

I don't like the name of it.
(cherry picked from commit b35bf7d51d76175e78b574df438aa8afc4c6cef3)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

include/vlc_interface.h

@@ -209,7 +209,7 @@ typedef enum vlc_dialog {
                          "*.m2t;*.m2ts;*.m4v;*.mkv;*.mov;*.mp2;*.mp4;*.mpeg;*.mpeg1;" \
                          "*.mpeg2;*.mpeg4;*.mpg;*.mts;*.mxf;*.nsv;*.nuv;" \
                          "*.ogg;*.ogm;*.ogv;*.ogx;*.ps;" \
-                         "*.rec;*.rm;*.rmvb;*.tod;*.ts;*.vob;*.vro;*.wmv"
+                         "*.rec;*.rm;*.rmvb;*.tod;*.ts;*.vob;*.vro;*.webm;*.wmv"
 
 #define EXTENSIONS_PLAYLIST "*.asx;*.b4s;*.ifo;*.m3u;*.m3u8;*.pls;*.ram;*.rar;*.sdp;*.vlc;*.xspf;*.zip"