Factor out wxTextMeasureBase::GetEmptyLineHeight()

No real changes, just refactor to extract a trivial helper function.

include/wx/private/textmeasure.h

@@ -128,6 +128,10 @@ protected:
                            wxCoord *descent = NULL,
                            wxCoord *externalLeading = NULL);
 
+    // Get line height: used when the line is empty because CallGetTextExtent()
+    // would just return (0, 0) in this case.
+    int GetEmptyLineHeight();
+
     // Return a valid font: if one was given to us in the ctor, use this one,
     // otherwise use the current font of the associated wxDC or wxWindow.
     wxFont GetFont() const;

src/common/textmeasurecmn.cpp

@@ -100,6 +100,13 @@ void wxTextMeasureBase::GetTextExtent(const wxString& string,
     CallGetTextExtent(string, width, height, descent, externalLeading);
 }
 
+int wxTextMeasureBase::GetEmptyLineHeight()
+{
+    int dummy, height;
+    CallGetTextExtent(wxS("W"), &dummy, &height);
+    return height;
+}
+
 void wxTextMeasureBase::GetMultiLineTextExtent(const wxString& text,
                                                wxCoord *width,
                                                wxCoord *height,
@@ -136,12 +143,9 @@ void wxTextMeasureBase::GetMultiLineTextExtent(const wxString& text,
                 if ( !heightLineDefault )
                     heightLineDefault = heightLine;
 
+                // and if we hadn't had any previous one neither, compute it now
                 if ( !heightLineDefault )
-                {
+                    heightLineDefault = GetEmptyLineHeight();
-                    // but we don't know it yet - choose something reasonable
-                    int dummy;
-                    CallGetTextExtent(wxS("W"), &dummy, &heightLineDefault);
-                }
 
                 heightTextTotal += heightLineDefault;
             }