[core/zip] Properly account for HDRSIZE in R__zipZLIB

R__unzipZLIB is already properly subtracting it from srcsize.

core/zip/src/RZip.cxx

@@ -197,7 +197,7 @@ static void R__zipZLIB(int cxlevel, int *srcsize, char *src, int *tgtsize, char
     stream.avail_in  = (uInt)(*srcsize);
 
     stream.next_out  = (Bytef*)(&tgt[HDRSIZE]);
-    stream.avail_out = (uInt)(*tgtsize);
+    stream.avail_out = (uInt)(*tgtsize) - HDRSIZE;
 
     stream.zalloc    = (alloc_func)0;
     stream.zfree     = (free_func)0;