I just tried to compile package flphoto-1.3-8 with the GNU C compiler.

It said

Fl_CRW_Image.cxx:767: warning: operation on "prow" may be undefined

The source code is

        *prow++ = (*prow << 2) + ((c >> r) & 3);
 
I agree with the compiler.  Suggest new code

	{
        *prow = (*prow << 2) + ((c >> r) & 3);
		++prow;
	}