Ogre2 depth camera doesn't trigger point cloud event

**Original report ([archived issue](https://osrf-migration.github.io/ignition-gh-pages/#!/ignitionrobotics/ign-rendering/issues/49)) by Louise Poubel (Bitbucket: [chapulina](https://bitbucket.org/%7B5cfa2075-477b-4ded-bdb9-8d2479544ec4%7D/), GitHub: [chapulina](https://github.com/chapulina)).**

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# Prerequisites

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* Checked the Q&A board for common solutions: http://answers.gazebosim.org
* Checked that your issue isn't already filed.
* Checked that there is not already an Ignition package that provides the described functionality: https://ignitionrobotics.org/libs

# Description

If a callback is registered with [Ogre2DepthCamera::ConnectNewRgbPointCloud](https://github.com/ignitionrobotics/ign-rendering/blob/4d4a25983d8c6ef0b004d0531c95e9ddac571db7/ogre2/include/ignition/rendering/ogre2/Ogre2DepthCamera.hh#L94), it will never be called because the `newRgbPointCloud` is never triggered.

# Steps to Reproduce

1. Connect a callback to `ConnectNewRgbPointCloud`
1. Update the camera and see that the callback is not called.

**Expected behavior:**

The callback is triggered

**Actual behavior:**

Nothing

**Reproduces how often:**

100%

# Versions

2

# Additional Information

Ogre 1 calls the event, but Ogre2 doesn't:

```
$ grep -r "newRgbPointCloud" .
./ogre/src/OgreDepthCamera.cc: const std::string &)> newRgbPointCloud;
./ogre/src/OgreDepthCamera.cc: this->dataPtr->newRgbPointCloud(
./ogre/src/OgreDepthCamera.cc: return this->dataPtr->newRgbPointCloud.Connect(_subscriber);
./ogre2/src/Ogre2DepthCamera.cc: const std::string &)> newRgbPointCloud;
./ogre2/src/Ogre2DepthCamera.cc: return this->dataPtr->newRgbPointCloud.Connect(_subscriber);
```