Ensure that scrollbar GtkRange page increment is set to a positive value

It should not be less than the step increment, which is always one.
See #18688

src/gtk/scrolbar.cpp

@@ -201,12 +201,15 @@ void wxScrollBar::SetThumbPosition( int viewStart )
 
 void wxScrollBar::SetScrollbar(int position, int thumbSize, int range, int pageSize, bool)
 {
-    if (range == 0)
+    if (range <= 0)
     {
         // GtkRange requires upper > lower
         range =
+        pageSize =
         thumbSize = 1;
     }
+    else if (pageSize <= 0)
+        pageSize = 1;
     g_signal_handlers_block_by_func(m_widget, (void*)gtk_value_changed, this);
     GtkRange* widget = GTK_RANGE(m_widget);
     GtkAdjustment* adj = gtk_range_get_adjustment(widget);

src/gtk/scrolwin.cpp

@@ -54,6 +54,8 @@ void wxScrollHelper::DoAdjustScrollbar(GtkRange* range,
     {
         upper = (virtSize + pixelsPerLine - 1) / pixelsPerLine;
         page_size = winSize / pixelsPerLine;
+        if (page_size == 0)
+            page_size = 1;
         *lines = upper;
         *linesPerPage = page_size;
     }

src/gtk/window.cpp

@@ -6011,6 +6011,8 @@ void wxWindowGTK::SetScrollbar(int orient,
         range =
         thumbVisible = 1;
     }
+    else if (thumbVisible <= 0)
+        thumbVisible = 1;
 
     g_signal_handlers_block_by_func(
         sb, (void*)gtk_scrollbar_value_changed, this);