ace2_inner: Fix efficiency of `rangeForLine()`

Returning `true` or `false` has no effect when iterating using
`Array.prototype.forEach`. This fixes a bug introduced in commit
b28bfe8e31.

src/static/js/ace2_inner.js

@@ -2162,16 +2162,13 @@ function Ace2Inner(editorInfo, cssManagers) {
       [-1, N + 1],
     ];
 
-    const rangeForLine = (i) => {
     // returns index of cleanRange containing i, or -1 if none
-      let answer = -1;
-      cleanRanges.forEach((r, idx) => {
-        if (i >= r[1]) return false; // keep looking
-        if (i < r[0]) return true; // not found, stop looking
-        answer = idx;
-        return true; // found, stop looking
-      });
-      return answer;
+    const rangeForLine = (i) => {
+      for (const [idx, r] of cleanRanges.entries()) {
+        if (i < r[0]) return -1;
+        if (i < r[1]) return idx;
+      }
+      return -1;
     };
 
     const removeLineFromRange = (rng, line) => {