warning fixes

unpaid_cost():  'shkp' might be used without being initialized.  That
sort of warning is sometimes wrong but was correct in this instance.

qt_Splash():  the Qt 6.2 warning suggests switching the argument for
setMask() from QBitmap() to fromPixmap() but that doesn't work with
5.11.  However, switching from setMask() to setPixmap() does work,
and results in a crisp splash image instead of the fuzzy one I
recently complained about.  I've no idea what the right QT_VERSION
check ought to be but another QLabel propery is documented as "added
in 4.2" and the pixmap one has no such mention so I picked Qt < 4
for the code that's been in use and Qt >= 4 for the new code.

src/shk.c

@@ -2420,7 +2420,7 @@ unpaid_cost(
     boolean include_contents)
 {
     struct bill_x *bp = (struct bill_x *) 0;
-    struct monst *shkp;
+    struct monst *shkp = 0;
     char *shop;
     long amt = 0L;
 

win/Qt/qt_bind.cpp

@@ -125,7 +125,14 @@ NetHackQtBind::qt_Splash()
         vb->addWidget(capt);
         capt->setAlignment(Qt::AlignCenter);
         lsplash->setFixedSize(pm.size());
+
+#if QT_VERSION < 0x040000
+        // if used on 5.11, this produces a fuzzy image
         lsplash->setMask(QBitmap(pm));
+#else
+        // required for 6.2; on 5.11, this produces a crisp image
+        lsplash->setPixmap(pm);
+#endif
 
 #if QT_VERSION < 0x060000
         QSize screensize = QApplication::desktop()->size();