SIGFPE in sprite viewer

[07151129]

When trying to enter magnification factor from keyboard, mGBA (at git HEAD) crashes with the following backtrace:

Exception Type:        EXC_ARITHMETIC (SIGFPE)
Exception Codes:       EXC_I386_DIV (divide by zero)
Exception Note:        EXC_CORPSE_NOTIFY

Termination Signal:    Floating point exception: 8
Termination Reason:    Namespace SIGNAL, Code 0x8
Terminating Process:   exc handler [39218]

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   com.endrift.mgba-qt           	0x000000010a753d23 QGBA::TilePainter::setTileCount(int) + 99
1   org.qt-project.QtCore         	0x000000010d84ab73 QMetaObject::activate(QObject*, int, int, void**) + 2395
2   org.qt-project.QtWidgets      	0x000000010b48642e 0x10b324000 + 1451054
3   org.qt-project.QtWidgets      	0x000000010b47fc86 0x10b324000 + 1424518
4   org.qt-project.QtWidgets      	0x000000010b482c4e 0x10b324000 + 1436750
5   org.qt-project.QtCore         	0x000000010d84ab73 QMetaObject::activate(QObject*, int, int, void**) + 2395
6   org.qt-project.QtWidgets      	0x000000010b437c2f 0x10b324000 + 1129519
7   org.qt-project.QtCore         	0x000000010d84ab73 QMetaObject::activate(QObject*, int, int, void**) + 2395
8   org.qt-project.QtWidgets      	0x000000010b439485 QWidgetLineControl::finishChange(int, bool, bool) + 583
9   org.qt-project.QtWidgets      	0x000000010b43d5c0 QWidgetLineControl::processKeyEvent(QKeyEvent*) + 1028
10  org.qt-project.QtWidgets      	0x000000010b434ebc QLineEdit::keyPressEvent(QKeyEvent*) + 32
11  org.qt-project.QtWidgets      	0x000000010b35ff5a QWidget::event(QEvent*) + 1314
12  org.qt-project.QtWidgets      	0x000000010b4343e0 QLineEdit::event(QEvent*) + 600
13  org.qt-project.QtWidgets      	0x000000010b481b2c QAbstractSpinBox::keyPressEvent(QKeyEvent*) + 1164
14  org.qt-project.QtWidgets      	0x000000010b35ff5a QWidget::event(QEvent*) + 1314
15  org.qt-project.QtWidgets      	0x000000010b480c36 QAbstractSpinBox::event(QEvent*) + 346
16  org.qt-project.QtWidgets      	0x000000010b331d33 QApplicationPrivate::notify_helper(QObject*, QEvent*) + 269
17  org.qt-project.QtWidgets      	0x000000010b3334dd QApplication::notify(QObject*, QEvent*) + 1937
18  org.qt-project.QtCore         	0x000000010d8254c4 QCoreApplication::notifyInternal2(QObject*, QEvent*) + 154
19  org.qt-project.QtWidgets      	0x000000010b377657 0x10b324000 + 341591
20  org.qt-project.QtWidgets      	0x000000010b376e8f 0x10b324000 + 339599
21  org.qt-project.QtWidgets      	0x000000010b331d33 QApplicationPrivate::notify_helper(QObject*, QEvent*) + 269
22  org.qt-project.QtWidgets      	0x000000010b333018 QApplication::notify(QObject*, QEvent*) + 716
23  org.qt-project.QtCore         	0x000000010d8254c4 QCoreApplication::notifyInternal2(QObject*, QEvent*) + 154
24  org.qt-project.QtGui          	0x000000010b82908b QGuiApplicationPrivate::processKeyEvent(QWindowSystemInterfacePrivate::KeyEvent*) + 161
25  org.qt-project.QtGui          	0x000000010b8176c5 QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 149
26  org.qt-project.QtGui          	0x000000010b8144c9 QWindowSystemInterface::flushWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 525
27  libqcocoa.dylib               	0x0000000112ae59a5 0x112ac6000 + 129445
28  libqcocoa.dylib               	0x0000000112ae5b3d 0x112ac6000 + 129853
29  com.apple.AppKit              	0x00007fff42284436 -[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:] + 6946
30  com.apple.AppKit              	0x00007fff422826c9 -[NSWindow(NSEventRouting) sendEvent:] + 481
31  libqcocoa.dylib               	0x0000000112ae97d5 0x112ac6000 + 145365
32  com.apple.AppKit              	0x00007fff4212030b -[NSApplication(NSEvent) sendEvent:] + 2823
33  libqcocoa.dylib               	0x0000000112aeecca 0x112ac6000 + 167114
34  com.apple.AppKit              	0x00007fff4210d19d -[NSApplication run] + 755
35  libqcocoa.dylib               	0x0000000112aebdd1 0x112ac6000 + 155089
36  org.qt-project.QtCore         	0x000000010d821fe0 QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) + 318
37  org.qt-project.QtCore         	0x000000010d825978 QCoreApplication::exec() + 116
38  com.endrift.mgba-qt           	0x000000010a692d82 main + 5138
39  libdyld.dylib                 	0x00007fff71e04ed9 start + 1

This only seems to happen for hidden objects in OAM.