muxedit: silence some uninitialized warnings
muxedit: silence some uninitialized warnings

src/mux/muxedit.c:490: warning: 'x_offset' may be used uninitialized in this function
src/mux/muxedit.c:490: warning: 'y_offset' may be used uninitialized in this function

Change-Id: I4fd27f717e59a556354d0560b633d0edafe7a4d8
(cherry picked from commit 14cd5c6c401fd769995030c135d07fae56f2ecca)

yohunl/libwebp,rxl194/libwebp,Maria1099/webm.libwebp,reimaginemedia/webm.libwebp,kleopatra999/webm.libwebp,iniwf/webm.libwebp,ttyangf/libwebp,matanbs/webm.libwebp,kim42083/webm.libwebp,redengineer/libwebp,ttyangf/libwebp,kim42083/webm.libwebp,redengineer/libwebp,kalli123/webm.libwebp,appunite/libwebp,Aexyn/libwebp,Tekserve/libwebp,appunite/libwebp,keane83/BLE_IM,altogother/webm.libwebp,Aexyn/libwebp,comoyo/gonzo-libwebp,gshORTON/webm.libwebp,cysp/libwebp,Acidburn0zzz/webm.libwebp,cysp/libwebp,Suvarna1488/webm.libwebp,kleopatra999/webm.libwebp,Maria1099/webm.libwebp,zofuthan/libwebp,comoyo/gonzo-libwebp,ericmckean/webm.libwebp,zofuthan/libwebp,Maria1099/webm.libwebp,jiehu5114/libwebp,ericmckean/webm.libwebp,PKRoma/libwebp,jacklicn/libwebp,appunite/libwebp,jacklicn/libwebp,comoyo/gonzo-libwebp,iniwf/webm.libwebp,jacklicn/libwebp,ttyangf/libwebp,imazen/libwebp,gshORTON/webm.libwebp,appunite/libwebp,yohunl/libwebp,matanbs/webm.libwebp,webmproject/libwebp,comoyo/gonzo-libwebp,Suvarna1488/webm.libwebp,kalli123/webm.libwebp,abwiz0086/webm.libwebp,comoyo/gonzo-libwebp,PKRoma/libwebp,PKRoma/libwebp,yohunl/libwebp,Tekserve/libwebp,Aexyn/libwebp,webmproject/libwebp,iniwf/webm.libwebp,rxl194/libwebp,Acidburn0zzz/webm.libwebp,ya7lelkom/libwebp,zofuthan/libwebp,altogother/webm.libwebp,Aexyn/libwebp,Acidburn0zzz/webm.libwebp,ya7lelkom/libwebp,altogother/webm.libwebp,ericmckean/webm.libwebp,webmproject/libwebp,comoyo/gonzo-libwebp,webmproject/libwebp,appunite/libwebp,ericmckean/webm.libwebp,cysp/libwebp,Tekserve/libwebp,zofuthan/libwebp,Acidburn0zzz/webm.libwebp,kleopatra999/webm.libwebp,kalli123/webm.libwebp,Tekserve/libwebp,gshORTON/webm.libwebp,abwiz0086/webm.libwebp,matanbs/webm.libwebp,altogother/webm.libwebp,reimaginemedia/webm.libwebp,redengineer/libwebp,abwiz0086/webm.libwebp,iniwf/webm.libwebp,Suvarna1488/webm.libwebp,reimaginemedia/webm.libwebp,PKRoma/libwebp,imazen/libwebp,keane83/BLE_IM,abwiz0086/webm.libwebp,abwiz0086/webm.libwebp,appunite/libwebp,cysp/libwebp,ericmckean/webm.libwebp,kim42083/webm.libwebp,jiehu5114/libwebp,ya7lelkom/libwebp,comoyo/gonzo-libwebp,gshORTON/webm.libwebp,matanbs/webm.libwebp,jiehu5114/libwebp,zofuthan/libwebp,Aexyn/libwebp,PKRoma/libwebp,ya7lelkom/libwebp,kleopatra999/webm.libwebp,keane83/BLE_IM,kleopatra999/webm.libwebp,gshORTON/webm.libwebp,Acidburn0zzz/webm.libwebp,iniwf/webm.libwebp,kim42083/webm.libwebp,jiehu5114/libwebp,jiehu5114/libwebp,imazen/libwebp,rxl194/libwebp,Maria1099/webm.libwebp,keane83/BLE_IM,Maria1099/webm.libwebp,redengineer/libwebp,yohunl/libwebp,rxl194/libwebp,webmproject/libwebp,yohunl/libwebp,jacklicn/libwebp,imazen/libwebp,kim42083/webm.libwebp,redengineer/libwebp,kalli123/webm.libwebp,keane83/BLE_IM,Suvarna1488/webm.libwebp,matanbs/webm.libwebp,kalli123/webm.libwebp,imazen/libwebp,altogother/webm.libwebp,ya7lelkom/libwebp,reimaginemedia/webm.libwebp,reimaginemedia/webm.libwebp,PKRoma/libwebp,jacklicn/libwebp,Suvarna1488/webm.libwebp,ttyangf/libwebp,rxl194/libwebp,ttyangf/libwebp