Split the batch metrics loop on the glyf branch instead of per glyph

The glyf check does not vary across the run, so it belongs above the loop
rather than inside it. Splitting it also lets the bounds buffer live only
in the branch that reads it, which drops the zero-length allocation that
CFF / CFF2 fonts used to make just to satisfy the shared loop.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: Gillibald

src/Avalonia.Base/Media/GlyphTypeface.cs

@@ -828,25 +828,17 @@ public bool TryGetGlyphMetrics(ReadOnlySpan<ushort> glyphIndices, Span<GlyphMetr
                 return false;
             }
 
-            // Read all bounding boxes in one batch (spans fetched once), then combine. When
-            // the font has no glyf table, bearings fall back to hmtx/vmtx and the box is zero.
-            var hasGlyf = _glyfTable != null;
-
-            // No glyf table (CFF / CFF2) → no ink bounds to read; keep the buffer empty so
-            // those fonts don't allocate a per-glyph bounds array that is never used.
-            var boundsCount = hasGlyf ? glyphIndices.Length : 0;
-            Span<GlyphBounds> bounds = boundsCount <= 256
-                ? stackalloc GlyphBounds[boundsCount]
-                : new GlyphBounds[boundsCount];
-
-            if (hasGlyf)
+            if (_glyfTable != null)
             {
-                _glyfTable!.GetGlyphBounds(glyphIndices, bounds);
-            }
+                // Read all bounding boxes in one batch, so the glyf and loca spans are fetched once
+                // for the whole run rather than per glyph.
+                Span<GlyphBounds> bounds = glyphIndices.Length <= 256
+                    ? stackalloc GlyphBounds[glyphIndices.Length]
+                    : new GlyphBounds[glyphIndices.Length];
 
-            for (int i = 0; i < glyphIndices.Length; i++)
-            {
-                if (hasGlyf)
+                _glyfTable.GetGlyphBounds(glyphIndices, bounds);
+
+                for (int i = 0; i < glyphIndices.Length; i++)
                 {
                     var b = bounds[i];
 
@@ -860,7 +852,12 @@ public bool TryGetGlyphMetrics(ReadOnlySpan<ushort> glyphIndices, Span<GlyphMetr
                         AdvanceHeight = hasVertical ? vMetrics[i].AdvanceHeight : (ushort)0,
                     };
                 }
-                else
+            }
+            else
+            {
+                // No glyf table (CFF / CFF2): there are no ink bounds to read, so bearings fall
+                // back to hmtx/vmtx and the box stays zero. No bounds buffer is allocated either.
+                for (int i = 0; i < glyphIndices.Length; i++)
                 {
                     metrics[i] = new GlyphMetrics
                     {