Fix a another memory leak in etctool.

imgdec = (unsigned char*) malloc(expandedwidth*expandedheight*3);
is called before the if statement "if((f=fopen(dstfile,"wb")))"

If the file 'f' failed in the if statement, it would never be freed (since "free(imgdec)" was within that if block.
Merge pull request #43 from lioncash/master

Another memory leak fixed in etctool