Fixed two thumb size related bugs (see issue #346)

rtgui/thumbbrowserentrybase.cc

@@ -271,6 +271,9 @@ void ThumbBrowserEntryBase::resize (int h) {
         // dimensions of the info text
         getTextSizes (infow, infoh);
         preh -= infoh + textGap;
+
+        // If the text size was selected very high in preferences this may go negative
+        if (preh<0) preh=0;
     }
 
     calcThumbnailSize ();