TW-1678: segfault in ~ViewTask()

- Column::setStyle now validates column styles.
- Thanks to Daniel Shahaf.

src/columns/ColDue.cpp

@@ -52,7 +52,7 @@ ColumnDue::~ColumnDue ()
 // Note that you can not determine which gets called first.
 void ColumnDue::setStyle (const std::string& value)
 {
-  _style = value;
+  Column::setStyle (value);
 
   if (_style == "countdown" && _label == STRING_COLUMN_LABEL_DUE)
     _label = STRING_COLUMN_LABEL_COUNT;

src/columns/Column.cpp

@@ -247,6 +247,16 @@ void Column::renderHeader (
   }
 }
 
+////////////////////////////////////////////////////////////////////////////////
+void Column::setStyle (const std::string& style)
+{
+  if (style != "default" &&
+      std::find (_styles.begin (), _styles.end (), style) == _styles.end ())
+    throw format (STRING_COLUMN_BAD_FORMAT, _name, style);
+
+  _style = style;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 bool Column::validate (std::string& input)
 {

src/columns/Column.h

@@ -53,7 +53,7 @@ public:
   std::vector <std::string> styles () const   { return _styles;      }
   std::vector <std::string> examples () const { return _examples;    }
 
-  virtual void setStyle  (const std::string& value) { _style = value;  }
+  virtual void setStyle  (const std::string&);
   virtual void setLabel  (const std::string& value) { _label = value;  }
   virtual void setReport (const std::string& value) { _report = value; }