import model only if it has import for c#

modules/swagger-codegen/src/main/java/io/swagger/codegen/DefaultGenerator.java

@@ -430,6 +430,12 @@ public class DefaultGenerator extends AbstractGenerator implements Generator {
         }
 
         operations.put("imports", imports);
+
+        // add a flag to indicate whether there's any {{import}}
+        if (imports.size() > 0) {
+            operations.put("hasImport", true);
+        }
+
         config.postProcessOperations(operations);
         if (objs.size() > 0) {
             List<CodegenOperation> os = (List<CodegenOperation>) objs.get("operation");