Try to fix possible crash in cee3523

MKleusberg · MKleusberg · commit 60f3f4404a0d · 2020-02-16T15:04:13.000+01:00
This was spotted and mentioned by @mgrojo here: cee3523#commitcomment-37302574 It does not reproduce on my system, so this is my best attempt at fixing this issue.
diff --git a/src/ExtendedTableWidget.cpp b/src/ExtendedTableWidget.cpp
@@ -869,7 +869,7 @@ void ExtendedTableWidget::vscrollbarChanged(int value)
 
 int ExtendedTableWidget::numVisibleRows() const
 {
-    if(!isVisible())
+    if(!isVisible() || !model() || !verticalHeader())
         return 0;
 
     // Get the row numbers of the rows currently visible at the top and the bottom of the widget

Original file line number	Diff line number	Diff line change
`@@ -869,7 +869,7 @@ void ExtendedTableWidget::vscrollbarChanged(int value)`
`869`	`869`
`870`	`870`	`int ExtendedTableWidget::numVisibleRows() const`
`871`	`871`	`{`
`872`		`- if(!isVisible())`
	`872`	`+ if(!isVisible() \|\| !model() \|\| !verticalHeader())`
`873`	`873`	`return 0;`
`874`	`874`
`875`	`875`	`// Get the row numbers of the rows currently visible at the top and the bottom of the widget`