Fix range of pan controls.

Set default range to [0,1] since [0,0] is problematic and useless anyway.

libs/ardour/parameter_descriptor.cc

@@ -50,6 +50,7 @@ ParameterDescriptor::ParameterDescriptor(const Evoral::Parameter& parameter)
 		break;
 	case PanAzimuthAutomation:
 		normal = 0.5f; // there really is no _normal but this works for stereo, sort of
+		upper  = 1.0f;
 		break;
 	case PanWidthAutomation:
 		lower  = -1.0;
@@ -57,7 +58,8 @@ ParameterDescriptor::ParameterDescriptor(const Evoral::Parameter& parameter)
 		normal = 0.0f;
 		break;
 	case RecEnableAutomation:
-		/* default 0.0 - 1.0 is fine */
+		lower  = 0.0;
+		upper  = 1.0;
 		toggled = true;
 		break;
 	case PluginAutomation:

libs/evoral/evoral/ParameterDescriptor.hpp

@@ -27,7 +27,7 @@ struct ParameterDescriptor
 	ParameterDescriptor()
 		: normal(0.0)
 		, lower(0.0)
-		, upper(0.0)
+		, upper(1.0)
 		, toggled(false)
 	{}