Don't throw when a mesh shading is degenerated

The problem of throwing an error is that it removes an operation
from drawing list which can cause a rendering issue.

src/core/pattern.js

@@ -968,20 +968,13 @@ class MeshShading extends BaseShading {
   }
 
   getIR() {
-    const { bounds } = this;
-    // Ensure that the shading has non-zero width and height, to prevent errors
-    // in `pattern_helper.js` (fixes issue17848.pdf).
-    if (bounds[2] - bounds[0] === 0 || bounds[3] - bounds[1] === 0) {
-      throw new FormatError(`Invalid MeshShading bounds: [${bounds}].`);
-    }
-
     return [
       "Mesh",
       this.shadingType,
       this.coords,
       this.colors,
       this.figures,
-      bounds,
+      this.bounds,
       this.bbox,
       this.background,
     ];

src/display/pattern_helper.js

@@ -462,16 +462,20 @@ class MeshShadingPattern extends BaseShadingPattern {
     const boundsWidth = Math.ceil(this._bounds[2]) - offsetX;
     const boundsHeight = Math.ceil(this._bounds[3]) - offsetY;
 
-    const width = Math.min(
-      Math.ceil(Math.abs(boundsWidth * combinedScale[0] * EXPECTED_SCALE)),
-      MAX_PATTERN_SIZE
-    );
-    const height = Math.min(
-      Math.ceil(Math.abs(boundsHeight * combinedScale[1] * EXPECTED_SCALE)),
-      MAX_PATTERN_SIZE
-    );
-    const scaleX = boundsWidth / width;
-    const scaleY = boundsHeight / height;
+    // Ensure that the shading has non-zero width and height, to prevent errors
+    // in `pattern_helper.js` (fixes issue17848.pdf).
+    const width =
+      Math.min(
+        Math.ceil(Math.abs(boundsWidth * combinedScale[0] * EXPECTED_SCALE)),
+        MAX_PATTERN_SIZE
+      ) || 1;
+    const height =
+      Math.min(
+        Math.ceil(Math.abs(boundsHeight * combinedScale[1] * EXPECTED_SCALE)),
+        MAX_PATTERN_SIZE
+      ) || 1;
+    const scaleX = boundsWidth ? boundsWidth / width : 1;
+    const scaleY = boundsHeight ? boundsHeight / height : 1;
 
     const context = {
       coords: this._coords,

test/pdfs/.gitignore

@@ -884,3 +884,4 @@
 !form_two_pages.pdf
 !outlines_se.pdf
 !radial_gradients.pdf
+!mesh_shading_empty.pdf

test/test_manifest.json

@@ -13998,5 +13998,12 @@
     "md5": "80e8bed66b83928698f008c33de47edd",
     "rounds": 1,
     "type": "eq"
+  },
+  {
+    "id": "mesh_shading_empty",
+    "file": "pdfs/mesh_shading_empty.pdf",
+    "md5": "5a1bf9cb73010d84b47d91bb66bae27d",
+    "rounds": 1,
+    "type": "eq"
   }
 ]