Eeschema, fields_grid_table.cpp: fix a crash when the eeschema settings are not available.

It happens if the svhematic is not open when opening the symbol editor.
Fix also a compil warning.

Fixes #6384
https://gitlab.com/kicad/code/kicad/issues/6384

eeschema/fields_grid_table.cpp

@@ -309,7 +309,9 @@ wxGridCellAttr* FIELDS_GRID_TABLE<T>::GetAttr( int aRow, int aCol, wxGridCellAtt
             wxString fn = GetValue( aRow, FDC_NAME );
 
             SCHEMATIC_SETTINGS* settings = m_frame->Prj().GetProjectFile().m_SchematicSettings;
-            const TEMPLATE_FIELDNAME* templateFn = settings->m_TemplateFieldNames.GetFieldName( fn );
+
+            const TEMPLATE_FIELDNAME* templateFn =
+                    settings ? settings->m_TemplateFieldNames.GetFieldName( fn ) : nullptr;
 
             if( templateFn && templateFn->m_URL )
             {

pcbnew/pcb_shape.h

@@ -106,6 +106,9 @@ public:
         case S_ARC:
         case S_CURVE:
             return false;
+
+        case S_LAST:    // Sentinel
+            break;
         }
 
         return false;   // Make compil happy