clean-up SourceFileRange::as_str (#15401)

changelog: none

Author: llogiq

clippy_utils/src/source.rs

@@ -342,11 +342,8 @@ impl SourceFileRange {
     /// Attempts to get the text from the source file. This can fail if the source text isn't
     /// loaded.
     pub fn as_str(&self) -> Option<&str> {
-        self.sf
-            .src
-            .as_ref()
-            .map(|src| src.as_str())
-            .or_else(|| self.sf.external_src.get().and_then(|src| src.get_source()))
+        (self.sf.src.as_ref().map(|src| src.as_str()))
+            .or_else(|| self.sf.external_src.get()?.get_source())
             .and_then(|x| x.get(self.range.clone()))
     }
 }