Fix tesselation of PathShape with NaN values

[TihonovNV]

Currently PathShapes with NaN values skip too many line segments around NaN point.

For example, the following PathShape

[
    pos2(10.0, 290.0),
    pos2(30.0, 270.0),
    pos2(50.0, 250.0),
    pos2(70.0, 230.0),
    pos2(90.0, f32::NAN),
    pos2(110.0, 190.0),
    pos2(130.0, 170.0),
    pos2(150.0, 150.0),
]

is drawn like that (skipping one segment before and after NaN point):

I made a small change to tessellate disconnected segments of PathShape separately:

Additionally, closed PathShape will not be tessellated if it contains NaNs.

• Closes epaint: Handle NaNs in Path #5397
• I have followed the instructions in the PR template

There is the same issue in egui_plot (emilk/egui_plot#131), I will fix it when this PR will be merged

[github-actions]

Preview is being built...

Preview will be available at https://egui-pr-preview.github.io/pr/7654-fix-nan-plotting

View snapshot changes at kitdiff