add method to determine if a capacity is valid

svn path=/trunk/extragear/sysadmin/partitionmanager/; revision=887292

src/util/capacity.cpp

@@ -171,6 +171,14 @@ QString Capacity::unitName(Unit u)
 	return unitNames[u];
 }
 
+/** Determine if the capacity is valid.
+	@return true if it is valid
+*/
+bool Capacity::isValid() const
+{
+	return m_Size >= 0;
+}
+
 QString Capacity::toStringInternal(qint64 unitSize) const
 {
 	if (m_Size < 0)

src/util/capacity.h

@@ -65,6 +65,8 @@ class Capacity
 		QString unitName() const;
 		Unit bestUnit() const;
 
+		bool isValid() const;
+
 		static const QString& invalidString() { return m_InvalidString; } /**< @return string representing an invalid capacity */
 		static QString unitName(Unit u);
 		static qint64 unitFactor(Unit from, Unit to);