[C#] Generate field not present condition checks using member field for _actingVersion. Issue #543.

Author: mjpt777

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/csharp/CSharpGenerator.java

@@ -697,7 +697,7 @@ private CharSequence generateArrayFieldNotPresentCondition(
         }
 
         return String.format(
-            indent + INDENT + INDENT + "if (actingVersion < %d) return 0;\n\n",
+            indent + INDENT + INDENT + "if (_actingVersion < %d) return 0;\n\n",
             sinceVersion);
     }
 
@@ -711,7 +711,7 @@ private CharSequence generateTypeFieldNotPresentCondition(
         }
 
         return String.format(
-            indent + INDENT + INDENT + "if (actingVersion < %d) return null;\n\n",
+            indent + INDENT + INDENT + "if (_actingVersion < %d) return null;\n\n",
             sinceVersion);
     }