Fixed android super.img loop download 52byte after some block

request_data change return value, which only contain requested
data region. sparse image to sparse image convert code has problem
at while(off < pos). off just request data offset. pos is whole
file's offset. off should add start point.

Signed-off-by: Frank Li <frank.li@nxp.com>

libuuu/fastboot.cpp

@@ -845,7 +845,7 @@ int FBFlashCmd::run(CmdCtx *ctx)
 					nt.total = startblock;
 					call_notify(nt);
 
-				} while (off < pos);
+				} while (off + oldpos < pos);
 			}
 		}