Fix going to a position in the simple editor with one line of code

Off-by-one errors are the worst.

Author: shepmaster

ui/frontend/editor/SimpleEditor.tsx

@@ -15,11 +15,9 @@ class CodeByteOffsets {
 
   public lineToOffsets(line: number) {
     const precedingBytes = this.bytesBeforeLine(line);
+    const nextPrecedingBytes = this.bytesBeforeLine(line + 1);
 
-    const highlightedLine = this.lines[line];
-    const highlightedBytes = highlightedLine.length;
-
-    return [precedingBytes, precedingBytes + highlightedBytes];
+    return [precedingBytes, nextPrecedingBytes];
   }
 
   public rangeToOffsets(start: Position, end: Position) {
@@ -40,7 +38,7 @@ class CodeByteOffsets {
     const precedingLines = this.lines.slice(0, line);
 
     // Add one to account for the newline we split on and removed
-    return precedingLines.map((l) => l.length + 1).reduce((a, b) => a + b);
+    return precedingLines.map((l) => l.length + 1).reduce((a, b) => a + b, 0);
   }
 }