fix to Go client template to address localVarFile error

Author: Peter Saffrey

modules/swagger-codegen/src/main/resources/go/api.mustache

@@ -148,8 +148,8 @@ func (a *{{{classname}}}Service) {{{nickname}}}(ctx context.Context{{#hasParams}
 {{#hasFormParams}}
 {{#formParams}}
 {{#isFile}}
-{{^required}}
 	var localVarFile {{dataType}}
+{^required}}
 	if localVarOptionals != nil && localVarOptionals.{{vendorExtensions.x-exportParamName}}.IsSet() {
 		localVarFileOk := false
 		localVarFile, localVarFileOk = localVarOptionals.{{vendorExtensions.x-exportParamName}}.Value().({{dataType}})