Fix T78186: Dyntopo panel error with tools that dont have a brush

Maniphest Tasks: T78186

Differential Revision: https://developer.blender.org/D8120

Fix T78401: Convert Mesh to Grease Pencil with empty material slot crashes

Also create the 'simple fill' in case there are only empty material
slots.

Maniphest Tasks: T78401

Differential Revision: https://developer.blender.org/D8151

Fix T78415: Particle Edit mode Add brush with a radius > 181px crashes

Caused by short overflow, change to int instead.

Maniphest Tasks: T78415

Differential Revision: https://developer.blender.org/D8148

Fix T77942: Add Cube scales immediately upon creation after changing Size attribute on prior Add Cube command

Always use the default size here, since desired bounds have been set
interactively, it does not make sense to use a different size from a
previous command.

Maniphest Tasks: T77942

Differential Revision: https://developer.blender.org/D8056

Fix T77764: VSE: snap strip to current frame does not move associated
effect strips keyframes along

Maniphest Tasks: T77764

Differential Revision: https://developer.blender.org/D7996

Fix T77957: Height change in Camera Properties column when changing lens type

Remove unneeded extra column from perspective type properties.

Maniphest Tasks: T77957

Differential Revision: https://developer.blender.org/D8060

Fix T77047: Dyntopo Sample detail size on hidden mesh causes crash

The `Toolbar` and `Sidebar` hide the corresponding panel
`VIEW3D_PT_sculpt_dyntopo` by polling for context.sculpt_object and
context.tool_settings.sculpt. In the Active Tool in the Properties
Editor this poll does not return False though, thus the
sample_detail_size is possible from there.

Second security check (the operator poll `SCULPT_mode_poll`) checks the
active object -- that is still valid even if hidden, so we are allowed
to execute the operator. However the active object becomes NULL once the
area is switched in `sample_detail()` -- see `CTX_wm_area_set`), leading
to the crash.

Dont think there is a quick and easy way to do this in the poll from the
Properties Editor, so just check for a valid active abject in the
operator and return OPERATOR_CANCELLED if we dont have it.

Maniphest Tasks: T77047

Differential Revision: https://developer.blender.org/D7832

Fix T77356: Texture Preview not taking alpha into account

Since rB329b4c3363e4 a texture preview is not rendered through the
preview.blend and a renderengine anymore [unlike materials etc.]

Alpha wasnt handled in that commit, take that into account now.

sidenote: not sure if we should be looking into drawing alpha with a
checkerboard in the background for texture previews (see texture
previews elsewhere)?

sidenote 2: might also be good to document where the "calculate" and
"invert" alpha options are still used? [looks a bit inconsistent:
compositor uses it, Image Editor as well as Render Engines dont?]

Maniphest Tasks: T77356

Differential Revision: https://developer.blender.org/D7929

Fix T77068: UV Proportional Edit "Connected Only" option affects UV
clipping (even if the proportional edit itself is disabled)

Checking T_PROP_EDIT_ALL returns true for _any_ of the options, so just
check for T_PROP_EDIT.

Note: this might expand to other similar checks (e.g. header text)

Maniphest Tasks: T77068

Differential Revision: https://developer.blender.org/D7927

Fix T77264: Mantaflow: Liquid checkbox doesn't turn on while switching
between fluid types

When switching to gas, the fluids were not actually destroyed, leading to
the situation that they were then destroyed when actually switching to
liquid.

Maniphest Tasks: T77264

Differential Revision: https://developer.blender.org/D7907