fix(octave): guard isvalid calls so Octave CI passes (#146)

* fix(octave): guard isvalid in refreshActivePageWidgetsAfterResize_

Octave 7+ has no isvalid() for classdef handles, so the three unguarded
isvalid(w) / isvalid(w.FastSenseObj) calls in DashboardEngine line 2022
and 2045/2048 broke Octave CI (test_engine_preview_nbuckets_reset).
Inline an isOctave flag and short-circuit the check on Octave; behaviour
unchanged on MATLAB.

* fix(octave): guard isvalid in FastSenseWidget.autoScaleY_

Octave 7+ has no isvalid() for classdef handles, so the unguarded
isvalid(obj.FastSenseObj) check in autoScaleY_ broke every test that
renders a FastSenseWidget or calls setYLimitMode (testDetectStaleWithFrozenSensor,
testRefreshTriggers*, test_set_y_limit_mode_*, test_dashboard_preview_envelope).
Inline an isOctave flag and short-circuit on Octave.

* fix(octave): guard isvalid in syncYLimitButtonsState_

Octave 7+ has no isvalid() for classdef handles. Once autoScaleY_ is
fixed, dashboard tests proceed to addYLimitButtons_ which calls
syncYLimitButtonsState_ — the unguarded isvalid(w) on the cached widget
handle would then throw. Inline isOctave and short-circuit on Octave.

Author: HanSur94

libs/Dashboard/DashboardEngine.m

@@ -2016,10 +2016,13 @@ function refreshActivePageWidgetsAfterResize_(obj)
                 return;
             end
             ws = obj.activePageWidgets();
+            isOctave = exist('OCTAVE_VERSION', 'builtin') ~= 0;
             % --- Pass 1: cheap data re-push ---
             for i = 1:numel(ws)
                 w = ws{i};
-                if isempty(w) || ~isvalid(w)
+                % Octave 7+ has no isvalid() for classdef handles, so treat
+                % as valid there and rely on downstream guards / try-catch.
+                if isempty(w) || (~isOctave && ~isvalid(w))
                     continue;
                 end
                 if ~w.Realized || isempty(w.hPanel) || ~ishandle(w.hPanel)
@@ -2042,10 +2045,10 @@ function refreshActivePageWidgetsAfterResize_(obj)
             stillWhite = false;
             for i = 1:numel(ws)
                 w = ws{i};
-                if isempty(w) || ~isvalid(w) || ~isa(w, 'FastSenseWidget')
+                if isempty(w) || (~isOctave && ~isvalid(w)) || ~isa(w, 'FastSenseWidget')
                     continue;
                 end
-                if isempty(w.FastSenseObj) || ~isvalid(w.FastSenseObj) || ~w.FastSenseObj.IsRendered
+                if isempty(w.FastSenseObj) || (~isOctave && ~isvalid(w.FastSenseObj)) || ~w.FastSenseObj.IsRendered
                     continue;
                 end
                 if ~obj.isWidgetLineWhite_(w)

libs/Dashboard/DashboardLayout.m

@@ -1035,7 +1035,10 @@ function syncYLimitButtonsState_(bar, mode)
             inactiveBg = [];
             if isfield(ud, 'YLimitWidget') && ~isempty(ud.YLimitWidget)
                 w = ud.YLimitWidget;
-                if isobject(w) && isvalid(w) && ...
+                % Octave 7+ has no isvalid() for classdef handles; treat as
+                % valid there and rely on the property-access guards below.
+                isOctave = exist('OCTAVE_VERSION', 'builtin') ~= 0;
+                if isobject(w) && (isOctave || isvalid(w)) && ...
                         ~isempty(w.ParentTheme) && isstruct(w.ParentTheme) && ...
                         isfield(w.ParentTheme, 'ToolbarBackground')
                     inactiveBg = w.ParentTheme.ToolbarBackground;

libs/Dashboard/FastSenseWidget.m

@@ -450,7 +450,11 @@ function autoScaleY_(obj, y)
             if obj.UserZoomedY
                 return;
             end
-            if ~isempty(obj.FastSenseObj) && isvalid(obj.FastSenseObj) && ...
+            % Octave 7+ has no isvalid() for classdef handles, so treat the
+            % FastSense handle as valid there and let downstream property
+            % access surface real failures.
+            isOctave = exist('OCTAVE_VERSION', 'builtin') ~= 0;
+            if ~isempty(obj.FastSenseObj) && (isOctave || isvalid(obj.FastSenseObj)) && ...
                     strcmp(obj.FastSenseObj.LiveViewMode, 'follow')
                 return;
             end