fix(equalizer): bail out when canvas has no laid-out dimensions (#384)

drawCurve read offsetWidth/offsetHeight unconditionally. When the canvas
sits inside a collapsed <details> (SettingsSubSection) on first paint,
both are 0, innerW becomes negative, the points-loop never runs, and
points[0][0] throws. Linux WebKitGTK happens to lay out the details
expanded on first render; macOS WebKit does not, so the same code path
unmounted the entire React tree because there is no ErrorBoundary above
Settings.

Bail early when innerW or innerH is non-positive — the ResizeObserver
already triggers a redraw once the canvas gets real dimensions.

Closes #382.

src/components/Equalizer.tsx

@@ -38,10 +38,6 @@ function drawCurve(canvas: HTMLCanvasElement, gains: number[], accentColor: stri
   const dpr = window.devicePixelRatio || 1;
   const W = canvas.offsetWidth;
   const H = canvas.offsetHeight;
-  canvas.width = W * dpr;
-  canvas.height = H * dpr;
-  const ctx = canvas.getContext('2d')!;
-  ctx.scale(dpr, dpr);
 
   const fMin = 20, fMax = 20000;
   const dbMin = -13, dbMax = 13;
@@ -49,6 +45,16 @@ function drawCurve(canvas: HTMLCanvasElement, gains: number[], accentColor: stri
   const innerW = W - padL - padR;
   const innerH = H - padT - padB;
 
+  // Canvas hidden or not laid out yet (e.g. inside a collapsed <details> on macOS WebKit).
+  // Bail before allocating an invalid back-buffer; ResizeObserver redraws when the canvas
+  // gets real dimensions.
+  if (innerW <= 0 || innerH <= 0) return;
+
+  canvas.width = W * dpr;
+  canvas.height = H * dpr;
+  const ctx = canvas.getContext('2d')!;
+  ctx.scale(dpr, dpr);
+
   const freqToX = (f: number) =>
     padL + (Math.log10(f / fMin) / Math.log10(fMax / fMin)) * innerW;
   const dbToY = (db: number) =>