fix a used before set warning

TODO

@@ -1,3 +1,9 @@
+- have this warning:
+
+im_histspec.c: In function 'im_histspec':
+im_histspec.c:101:6: warning: 'px' may be used uninitialized in this function
+[-Wuninitialized]
+im_histspec.c:79:6: note: 'px' was declared here:n ../his	
 
 - vips operation print could show operation flags as well, cf. "vips
   im_subtract"

libvips/histograms_lut/im_histspec.c

@@ -68,18 +68,18 @@
 static int
 match( IMAGE *in, IMAGE *ref, IMAGE *out )
 {
-	const int inpx = in->Xsize * in->Ysize;
-	const int refpx = ref->Xsize * ref->Ysize;
+	const guint64 inpx = (guint64) in->Xsize * in->Ysize;
+	const guint64 refpx = (guint64) ref->Xsize * ref->Ysize;
 	const int bands = in->Bands;	
 
 	unsigned int *inbuf;		/* in and ref, padded to same size */
 	unsigned int *refbuf;
 	unsigned int *outbuf;		/* Always output as uint */
 
-	int px;				/* Number of pixels */
-	int max;			/* px * bands */
+	guint64 px;			/* Number of pixels */
+	guint64 max;			/* px * bands */
 
-	int i, j;
+	guint64 i, j;
 
 	if( im_iocheck( in, out ) || 
 		im_iocheck( ref, out ) ||
@@ -98,6 +98,8 @@ match( IMAGE *in, IMAGE *ref, IMAGE *out )
 		px = 256;
 	else if( inpx <= 65536 && refpx <= 65536 )
 		px = 65536;
+	else 
+		px = IM_MAX( inpx, refpx );
 	max = px * bands;
 
 	/* Unpack to equal-sized buffers.

libvips/video/im_video_v4l1.c

@@ -45,7 +45,6 @@
 #include <unistd.h>
 #endif /*HAVE_UNISTD_H*/
 #include <errno.h>
-#include <assert.h>
 
 #include <sys/types.h>
 #include <sys/stat.h>