Fix unwrap error in overflowing int literal

Author: chenyukang

compiler/rustc_lint/src/types/literal.rs

@@ -274,7 +274,7 @@ fn lint_int_literal<'tcx>(
             return;
         }
 
-        let span = if negative { type_limits.negated_expr_span.unwrap() } else { span };
+        let span = if negative { type_limits.negated_expr_span.unwrap_or(span) } else { span };
         let lit = cx
             .sess()
             .source_map()

tests/ui/lint/lint-overflowing-int-136675.rs

@@ -0,0 +1,4 @@
+fn main() {
+    if let -129 = 0i8 {} //~ ERROR literal out of range for `i8`
+    let x: i8 = -129; //~ ERROR literal out of range for `i8`
+}

tests/ui/lint/lint-overflowing-int-136675.stderr

@@ -0,0 +1,21 @@
+error: literal out of range for `i8`
+  --> $DIR/lint-overflowing-int-136675.rs:2:12
+   |
+LL |     if let -129 = 0i8 {}
+   |            ^^^^
+   |
+   = note: the literal `-129` does not fit into the type `i8` whose range is `-128..=127`
+   = help: consider using the type `i16` instead
+   = note: `#[deny(overflowing_literals)]` on by default
+
+error: literal out of range for `i8`
+  --> $DIR/lint-overflowing-int-136675.rs:3:17
+   |
+LL |     let x: i8 = -129;
+   |                 ^^^^
+   |
+   = note: the literal `-129` does not fit into the type `i8` whose range is `-128..=127`
+   = help: consider using the type `i16` instead
+
+error: aborting due to 2 previous errors
+