sane.ds: Revise to match identity structures with partial information.

dlls/sane.ds/sane_main.c

@@ -645,19 +645,19 @@ static TW_UINT16 SANE_OpenDS( pTW_IDENTITY pOrigin, pTW_IDENTITY self) {
 
 	/* To make string as short as above */
 	lstrcpynA(name, sane_devlist[i]->vendor, sizeof(name)-1);
-	if (strcmp(name, self->Manufacturer))
+	if (self->Manufacturer && *self->Manufacturer && strcmp(name, self->Manufacturer))
 	    continue;
 	lstrcpynA(name, sane_devlist[i]->model, sizeof(name)-1);
-	if (strcmp(name, self->ProductFamily))
+	if (self->ProductFamily && *self->ProductFamily && strcmp(name, self->ProductFamily))
 	    continue;
         copy_sane_short_name(sane_devlist[i]->name, name, sizeof(name) - 1);
-	if (strcmp(name, self->ProductName))
+	if (self->ProductName && *self->ProductName && strcmp(name, self->ProductName))
 	    continue;
 	break;
     }
     if (!sane_devlist[i]) {
-	FIXME("Scanner not found? Using first one!\n");
-	i=0;
+	FIXME("Scanner not found.\n");
+	return TWRC_FAILURE;
     }
     status = psane_open(sane_devlist[i]->name,&activeDS.deviceHandle);
     if (status == SANE_STATUS_GOOD) {