fix(gui): give the clients list the macOS spacer column, and assert on it - #852

Two commits: the missing spacer on the clients list, and an assert so the next list cannot forget it.

The clients list had no spacer

CGenericClientListCtrl is the only list ported to wxDataViewCtrl that never got one. macOS hands leftover width to the last resizable column, so once the columns are wider than the control that column collapses to nothing. For Sources and Peers that is "Shares File List", and both panes sit in splitters that are routinely narrow.

One line: AppendSpacerColumn(m_columndata.n_columns). That id needs no further handling — GetItemColumnText(), GetItemBarFill() and CompareItemData() all already guard column >= n_columns.

Why the spacer is kept rather than removed

The obvious alternative was to drop the mechanism from all seven lists, on the theory that it was a workaround for the legacy wxLC_REPORT|wxSUNKEN_BORDER flags — wxLC_REPORT being the same bit as wxDV_VARIABLE_LINE_HEIGHT — which came off in 71bdb1a and #849.

A spacer-less build was tried and the collapse still reproduces, so that theory is wrong. The file-details list looked immune only because its two columns (370 + 70) do not overflow its dialog at their default widths, and columns are user-resizable, so that is a property of the defaults rather than of the list. #851 has the details.

The assert

Forgetting the spacer is invisible until somebody narrows a list far enough, which is how the clients list shipped without one. InitColumnState() is the single hook every list reaches unconditionally, so the check goes there, beside the existing column-id assert — both being failures that look like rendering bugs rather than programming errors.

Appending the spacer from the base instead was considered and does not work: it has to happen after the subclass' columns and before LoadColumnSettings(), and CSearchListCtrl calls LoadColumnSettings() only for its first tab, so every later tab would silently lose its spacer. CSearchListCtrl also derives from CMuleDataViewCtrl directly rather than through CMuleVirtualDataViewCtrl; InitColumnState() is common to both, so one assert covers all seven lists.

Testing

macOS Debug, amule + amulegui. Narrowing Sources and Peers until the columns overflow no longer collapses the last column. Every list opened once with the assert live — Downloads, Sources, Servers, Search including a second tab, Shared Files, Peers, Friends and the file-details dialog — with no assert raised. clang-format 18 and Tier-2 clang-tidy clean on the diff with 0 compiler errors.

Both the spacer and the assert are __WXOSX__-only, so GTK and MSW are unaffected.