GridLayer fails to load map tiles when `redraw` called at fractional zoom level

Checklist

• I’ve looked at the documentation to make sure the behavior isn’t documented and expected.
• I’m sure this is an issue with Leaflet, not with my app or other dependencies (Angular, Cordova, React, etc.).
• I’ve searched through the current issues to make sure this hasn’t been reported yet.
• I agree to follow the Code of Conduct that this project adheres to.

Steps to reproduce

Create a GridLayer and set the map zoom level to a fractional value, e.g. 2.5. Call the redraw() method on the grid layer. The layer makes requests with urls like:

<baseurl>/2.5/2/4.png

These requests fail, since the {z} value is typically only available in integer steps. So the map fails to load.

Expected behavior

The _tileZoom property should always be an integer value, so that the URL requested only resolves to integer values.

Current behavior

I believe the bug was introduced in this commit:

https://github.com/Leaflet/Leaflet/commit/2e8638761ca91506e3dc2b132da4c8185aab27f0

For example in _setView() the _tileZoom is round(zoom)

https://github.com/Leaflet/Leaflet/blob/c7d3e97d9ae3fada1f7ab047d4d56c06cec35d12/src/layer/tile/GridLayer.js#L552

I think this line ought to be:

var tileZoom = Math.round(this._clampZoom(this._map.getZoom()));

Minimal example reproducing the issue

No response

Environment

• Leaflet version: git main branch (also present in leaflet@1.8.0 from npm)
• Browser (with version): firefox-100.0-4.fc35.x86_64 (also seen in chrome / safari)
• OS/Platform (with version): Fedora 35 Linux (also seen on mac and windows)

[mhirsch]

I’ve been using a patched leaflet with the above one line change for 4 months without problems.

[raychanks]

As the gaps seem to be a separate issue, I will try to put together a PR for this one in the next couple of days.