[Swftools-common] bug in swfextract.c

[Gerard H. Pille]

In swfextract.c there is an  "if(pos)"  which should in fact be "if(pos>=0)",   
since findjpegboundary returns -1 when no boundary is found.  -1 is true, so 
when no boundery is found, the image is destroyed by the memmove.