Improve logical_viewport_size.

Addresses bevyengine#9770 (comment)

crates/bevy_render/src/camera/camera.rs

@@ -180,19 +180,15 @@ impl Camera {
     #[inline]
     pub fn logical_viewport_size(&self) -> Result<Vec2, LogicalViewportSizeError> {
         let viewport = self.viewport.as_ref();
-        let logical_viewport_size = viewport.and_then(|v| self.to_logical(v.physical_size));
-        if let Some(size) = logical_viewport_size {
+        if let Some(size) = viewport.and_then(|v| self.to_logical(v.physical_size)) {
+            Ok(size)
+        } else if let Some(size) = self.logical_target_size() {
             Ok(size)
         } else {
-            let logical_target_size = self.logical_target_size();
-            if let Some(size) = logical_target_size {
-                Ok(size)
-            } else {
-                Err(LogicalViewportSizeError {
-                    viewport_is_set: viewport.is_some(),
-                    target_info_is_set: self.computed.target_info.is_some(),
-                })
-            }
+            Err(LogicalViewportSizeError {
+                viewport_is_set: viewport.is_some(),
+                target_info_is_set: self.computed.target_info.is_some(),
+            })
         }
     }