Fix GAL check to account for shared function

Cairo Polyline and Polygon draw functions share a common routine.  While
Polygons must have 3 points to allow triangulation, a polyline (like our
text) need only have 2

common/gal/cairo/cairo_gal.cpp

@@ -1117,7 +1117,7 @@ void CAIRO_GAL_BASE::blitCursor( wxMemoryDC& clientDC )
 
 void CAIRO_GAL_BASE::drawPoly( const std::deque<VECTOR2D>& aPointList )
 {
-    wxCHECK( aPointList.size() > 2, /* void */ );
+    wxCHECK( aPointList.size() > 1, /* void */ );
 
     // Iterate over the point list and draw the segments
     std::deque<VECTOR2D>::const_iterator it = aPointList.begin();
@@ -1142,7 +1142,7 @@ void CAIRO_GAL_BASE::drawPoly( const std::deque<VECTOR2D>& aPointList )
 
 void CAIRO_GAL_BASE::drawPoly( const VECTOR2D aPointList[], int aListSize )
 {
-    wxCHECK( aListSize > 2, /* void */ );
+    wxCHECK( aListSize > 1, /* void */ );
 
     // Iterate over the point list and draw the segments
     const VECTOR2D* ptr = aPointList;
@@ -1166,7 +1166,7 @@ void CAIRO_GAL_BASE::drawPoly( const VECTOR2D aPointList[], int aListSize )
 
 void CAIRO_GAL_BASE::drawPoly( const SHAPE_LINE_CHAIN& aLineChain )
 {
-    wxCHECK( aLineChain.PointCount() > 2, /* void */ );
+    wxCHECK( aLineChain.PointCount() > 1, /* void */ );
 
     syncLineWidth();
 

common/gal/opengl/opengl_gal.cpp

@@ -1854,8 +1854,7 @@ void OPENGL_GAL::drawPolygon( GLdouble* aPoints, int aPointCount )
 
 void OPENGL_GAL::drawPolyline( const std::function<VECTOR2D (int)>& aPointGetter, int aPointCount )
 {
-    if( aPointCount < 2 )
-        return;
+    wxCHECK( aPointCount >= 2, /* return */ );
 
     currentManager->Color( strokeColor.r, strokeColor.g, strokeColor.b, strokeColor.a );
     int i;