Fix line info for multi-line strings (issue 22794)

pkg/analyzer/lib/src/generated/scanner.dart

Index: pkg/analyzer/lib/src/generated/scanner.dart
diff --git a/pkg/analyzer/lib/src/generated/scanner.dart b/pkg/analyzer/lib/src/generated/scanner.dart
index 13d77a5b6b9db34f99e5cbdca38c6ea2ee94cca4..273161025d2cce996497bef07df548c5f6f460cf 100644
--- a/pkg/analyzer/lib/src/generated/scanner.dart
+++ b/pkg/analyzer/lib/src/generated/scanner.dart
@@ -1474,7 +1474,6 @@ class Scanner {
     int next = _reader.advance();
     outer: while (next != -1) {
       while (next != quoteChar) {
-        next = _reader.advance();
         if (next == -1) {
           break outer;
         } else if (next == 0xD) {
@@ -1484,7 +1483,9 @@ class Scanner {
           }
           recordStartOfLine();
         } else if (next == 0xA) {
+          next = _reader.advance();
           recordStartOfLine();
+        } else {
           next = _reader.advance();
         }
       }