Fix #103451, find_width_of_character_at_span return width with 1 when reaching end

src/test/ui/parser/issue-103451.rs

@@ -0,0 +1,5 @@
+// error-pattern: this file contains an unclosed delimiter
+// error-pattern: expected value, found struct `R`
+struct R { }
+struct S {
+    x: [u8; R

src/test/ui/parser/issue-103451.stderr

@@ -0,0 +1,32 @@
+error: this file contains an unclosed delimiter
+  --> $DIR/issue-103451.rs:5:15
+   |
+LL | struct S {
+   |          - unclosed delimiter
+LL |     x: [u8; R
+   |        -      ^
+   |        |
+   |        unclosed delimiter
+
+error: this file contains an unclosed delimiter
+  --> $DIR/issue-103451.rs:5:15
+   |
+LL | struct S {
+   |          - unclosed delimiter
+LL |     x: [u8; R
+   |        -      ^
+   |        |
+   |        unclosed delimiter
+
+error[E0423]: expected value, found struct `R`
+  --> $DIR/issue-103451.rs:5:13
+   |
+LL | struct R { }
+   | ------------ `R` defined here
+LL | struct S {
+LL |     x: [u8; R
+   |             ^ help: use struct literal syntax instead: `R {}`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0423`.