Fixes this error, which would occur after `setPrecision` had been called
with a non-integer value.

```
Traceback (most recent call last):
  File "/usr/share/carla/carla_host.py", line 1442, in slot_handlePluginAddedCallback
    pitem = self.ui.listWidget.createItem(pluginId, self.fSavedSettings[CARLA_KEY_MAIN_CLASSIC_SKIN])
  File "/usr/share/carla/widgets/racklistwidget.py", line 241, in createItem
    return RackListItem(self, pluginId, useClassicSkin)
  File "/usr/share/carla/widgets/racklistwidget.py", line 86, in __init__
    self.recreateWidget(firstInit = True)
  File "/usr/share/carla/widgets/racklistwidget.py", line 176, in recreateWidget
    self.fWidget = createPluginSlot(self.fParent, self.host, self.fPluginId, self.fOptions)
  File "/usr/share/carla/carla_skin.py", line 2090, in createPluginSlot
    return PluginSlot_Default(parent, host, pluginId, skinColor, skinStyle)
  File "/usr/share/carla/carla_skin.py", line 1766, in __init__
    self.ready()
  File "/usr/share/carla/carla_skin.py", line 642, in ready
    paramWidget.setValue(self.host.get_internal_parameter_value(self.fPluginId, paramIndex))
  File "/usr/share/carla/widgets/scalabledial.py", line 282, in setValue
    QDial.setValue(self, qtValue)
TypeError: setValue(self, int): argument 2 has unexpected type 'float'
Error mapping plugin to canvas client: 16 Step Sequencer
```

Signed-off-by: falkTX <falktx@falktx.com>

Signed-off-by: falkTX <falktx@falktx.com>

Signed-off-by: falkTX <falktx@falktx.com>

Code preparation for scalable LEDs, Dials and Buttons

On some quirky Windows VST2 (old SWAM instruments) or old Linux ones (InsertPizHere plugins), a NaN parameter value would be sent.
This throws an error in the frontend code and prevent carla from creating the corresponding rack.
We workaround that by just returning early from PixmapDialsetValue() if the value is a NaN

Fixes #1143

Signed-off-by: falkTX <falktx@falktx.com>

Signed-off-by: falkTX <falktx@gmail.com>

Fixes #553

Sorry it took so long