Allow ModuleConfig.WithName("") to clear the module name (#1277)

We currently allow clearing other config with nil, such as FSConfig.
However, we missed a spot as internally we couldn't differentiate
between name never set, or explicitly set to empty. Now, when someone
sets the module name to empty, the name in the binary section is
ignored.

Signed-off-by: Adrian Cole <adrian@tetrate.io>

runtime.go

@@ -283,7 +283,7 @@ func (r *runtime) InstantiateModule(
 	}
 
 	name := config.name
-	if name == "" && code.module.NameSection != nil && code.module.NameSection.ModuleName != "" {
+	if !config.nameSet && code.module.NameSection != nil && code.module.NameSection.ModuleName != "" {
 		name = code.module.NameSection.ModuleName
 	}