Qt: Fix scrollbar arrows in memory view (fixes #1558)

CHANGES

@@ -97,6 +97,7 @@ Other fixes:
  - Core: Fix uninitialized memory issues with graphics caches
  - Vita: Fix analog controls (fixes mgba.io/i/1554)
  - Qt: Fix fast forward mute being reset (fixes mgba.io/i/1574)
+ - Qt: Fix scrollbar arrows in memory view (fixes mgba.io/i/1558)
 Misc:
  - GB Memory: Support manual SRAM editing (fixes mgba.io/i/1580)
 

src/platform/qt/MemoryModel.cpp

@@ -88,6 +88,19 @@ MemoryModel::MemoryModel(QWidget* parent)
 		update();
 	});
 
+	connect(verticalScrollBar(), &QSlider::actionTriggered, [this](int action) {
+		if (action == QSlider::SliderSingleStepAdd) {
+			++m_top;
+		} else if (action == QSlider::SliderSingleStepSub) {
+			--m_top;
+		} else {
+			return;
+		}
+		boundsCheck();
+		verticalScrollBar()->setValue(m_top);
+		update();
+	});
+
 	setRegion(0, 0x10000000, tr("All"));
 }