FOOTPRINT::GetBoundingHull(): avoid returning a empty hull SHAPE_POLY_SET,

when a footprint contains only texts.
empty SHAPE_POLY_SET creates most of time issues (crashes for instance) when
containing no data.
Ensure the returned SHAPE_POLY_SET contains a minimal hull (a 0.04 mm square)
Fixes #7026
https://gitlab.com/kicad/code/kicad/issues/7026

pcbnew/footprint.cpp

@@ -4,7 +4,7 @@
  * Copyright (C) 2017 Jean-Pierre Charras, jp.charras at wanadoo.fr
  * Copyright (C) 2015 SoftPLC Corporation, Dick Hollenbeck <dick@softplc.com>
  * Copyright (C) 2015 Wayne Stambaugh <stambaughw@gmail.com>
- * Copyright (C) 1992-2020 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 1992-2021 KiCad Developers, see AUTHORS.txt for contributors.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -712,6 +712,22 @@ SHAPE_POLY_SET FOOTPRINT::GetBoundingHull() const
         }
     }
 
+    // If there are some graphic items, build the actual hull.
+    // However if no items, create a minimal polygon (can happen if a footprint
+    // is created with no item: it contains only 2 texts.
+    if( rawPolys.OutlineCount() == 0 )
+    {
+        // generate a small dummy rectangular outline around the anchor
+        const int halfsize = Millimeter2iu( 0.02 );
+
+        rawPolys.NewOutline();
+        // add a square:
+        rawPolys.Append( GetPosition().x - halfsize,  GetPosition().y - halfsize );
+        rawPolys.Append( GetPosition().x + halfsize,  GetPosition().y - halfsize );
+        rawPolys.Append( GetPosition().x + halfsize,  GetPosition().y + halfsize );
+        rawPolys.Append( GetPosition().x - halfsize,  GetPosition().y + halfsize );
+    }
+
     std::vector<wxPoint> convex_hull;
     BuildConvexHull( convex_hull, rawPolys );