Prevent broken glyph assemblies when font data is incorrect (typst#6688)

Author: mkorje

crates/typst-layout/src/math/fragment.rs

@@ -739,7 +739,9 @@ fn assemble(
                 }
 
                 advance -= max_overlap;
-                growable += max_overlap - min_overlap;
+                // In case we have that max_overlap < min_overlap, ensure we
+                // don't decrease the value of growable.
+                growable += (max_overlap - min_overlap).max(Abs::zero());
             }
 
             full += advance;

tests/ref/math-stretch-min-overlap-exceeds-max.png

@@ -91,3 +91,12 @@ $ body^"text" $
   }
   $body^"long text"$
 }
+
+--- math-stretch-min-overlap-exceeds-max ---
+// Test that glyph assembly doesn't end up with negative lengths if the max
+// overlap calculated is less than the minConnectorOverlap.
+#show math.equation: set text(font: "STIX Two Math")
+// Warning: glyph has assembly parts with overlap less than minConnectorOverlap
+// Hint: its rendering may appear broken - this is probably a font bug
+// Hint: please file an issue at https://github.com/typst/typst/issues
+$ stretch(->)^"Gauss-Jordan Elimination" $