Volumetric Datasource does not realloc memory on dataset change

[moritz-h]

Describe the bug
When changing a dataset in the volumetric datasource no memory reallocation happens. If the new dataset is larger is will crash with a segfault. Here is a comment that explicitly states to just use the memory as is:

megamol/plugins/volume/src/VolumetricDataSource.cpp

Lines 638 to 642 in f0a06c6

	/*
	* The caller requests us to copy directly to the memory that is
	* provided in the call. We assume this memory to be contiguous
	* and large enough to hold all requested frames.
	*/

But someone must be responsible to do a reallocation somewhere if the dataset changes. With the initial loading the allocation happens in the if case right above the comment.

Steps To Reproduce

1. Load volume example (i.e. raycast_volume_renderer.lua)
2. Change file in volumetric datasource to a larger file (at runtime with GUI)
3. See segfault