webpmux: ReadImage: fix ptr free in error case
webpmux: ReadImage: fix ptr free in error case

allocate to temporaries and deal with output pointers in one place to
reduce casting.

Change-Id: Ib12d866440184315536f35a15eb5adeba7879ae7

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