Fixed invalid names of static field (variables).

Signed-off-by: Dimitar Dobrev <dpldobrev@yahoo.com>

src/Generator/Passes/CleanInvalidDeclNamesPass.cs

@@ -123,6 +123,12 @@ namespace CppSharp.Passes
             return base.VisitTypedefDecl(typedef);
         }
 
+        public override bool VisitVariableDecl(Variable variable)
+        {
+            variable.Name = CheckName(variable.Name);
+            return base.VisitVariableDecl(variable);
+        }
+
         private static void CheckEnumName(Enumeration @enum)
         {
             // If we still do not have a valid name, then try to guess one

tests/CSharpTemp/CSharpTemp.h

@@ -10,6 +10,8 @@ public:
     int& operator[](int i);
     int A;
 
+    static int null;
+
 protected:
     int P;
 };
@@ -265,4 +267,4 @@ public:
     void setIgnoredType(const IgnoredType<int>& value);
 private:
     IgnoredType<int> _ignoredType;
-};
+};