Bug 1858798 - Ignore any target snap points in the case of empty snapport. r=botond

Differential Revision: https://phabricator.services.mozilla.com/D226574

layout/generic/ScrollContainerFrame.cpp

@@ -7607,6 +7607,11 @@ ScrollSnapInfo ScrollContainerFrame::ComputeScrollSnapInfo() {
   result.InitializeScrollSnapStrictness(writingMode, disp);
 
   result.mSnapportSize = GetSnapportSize();
+  if (result.mSnapportSize.IsEmpty()) {
+    // Ignore any target snap points if the snapport is empty.
+    return result;
+  }
+
   CollectScrollPositionsForSnap(
       mScrolledFrame, mScrolledFrame, GetScrolledRect(), GetScrollPadding(),
       GetLayoutScrollRange(), writingMode, result, &mSnapTargets);

layout/generic/crashtests/1858798.html

@@ -0,0 +1,9 @@
+<style>
+* {
+  scroll-snap-align: end;
+  margin: 90% -100em;
+  scroll-snap-type: block mandatory ! important;
+  scroll-padding-inline: 54205949.19ch ! important;
+}
+</style>
+<math href="" autofocus>

layout/generic/crashtests/crashtests.list

@@ -815,5 +815,6 @@ asserts(0-14) load 1816574.html # Bug 1913247
 load 1821603.html
 load 1822118.html
 load 1825434.html
+load 1858798.html
 load 1915006.html
 asserts(0-85) load 1881375-1.html # bug 1890687 - assertions about fragmentation invariants, failing many times because the test runs in a loop