[winpr,clipboard] fix length of uri list

we overallocate the size, so ensure the result size only contains the
data actually used.

winpr/libwinpr/clipboard/synthetic_file.c

@@ -917,7 +917,8 @@ static void* convert_filedescriptors_to_file_list(wClipboard* clipboard, UINT32
 			}
 		}
 	}
-	winpr_HexDump(TAG, WLOG_DEBUG, (const BYTE*)dst, alloc);
+
+	alloc = strnlen(dst, alloc) + 1;
 	*pSize = (UINT32)alloc;
 	clipboard->fileListSequenceNumber = clipboard->sequenceNumber;
 	return dst;