Guard drawText() when X-bitmap fonts are used

If the fonts are mapped for some reason to X bitmap fonts,
the call to drawText() in the non-GUI thread will produce a crash.
Ensure that the rendering of the text is performed only if
the threaded font rendering is available - a rare event nowadays,
but still possible.

CCBUG: 248852

generators/dvi/special.cpp

@@ -20,6 +20,7 @@
 #include <kmimetype.h>
 
 #include <QFile>
+#include <QFontDatabase>
 #include <QImage>
 #include <QPainter>
 
@@ -421,11 +422,17 @@ void dviRenderer::epsf_special(const QString& cp)
     QFont f = foreGroundPainter->font();
     f.setPointSize(8);
     foreGroundPainter->setFont(f);
-    if (QFile::exists(EPSfilename))
-      foreGroundPainter->drawText (bbox, (int)(Qt::AlignCenter), EPSfilename);
-    else
-      foreGroundPainter->drawText (bbox, (int)(Qt::AlignCenter),
-                                i18n("File not found: \n %1", EPSfilename_orig));
+    /* if the fonts are mapped for some reason to X bitmap fonts,
+       the call to drawText() in the non-GUI thread will produce a crash.
+       Ensure that the rendering of the text is performed only if
+       the threaded font rendering is available */
+    if (QFontDatabase::supportsThreadedFontRendering()) {
+      if (QFile::exists(EPSfilename))
+        foreGroundPainter->drawText (bbox, (int)(Qt::AlignCenter), EPSfilename);
+      else
+        foreGroundPainter->drawText (bbox, (int)(Qt::AlignCenter),
+                                     i18n("File not found: \n %1", EPSfilename_orig));
+    }
     foreGroundPainter->restore();
   }