Update some comments for expandTypeIntoLeafProjectionPaths in Projection.h

Author: trentxintong

include/swift/SIL/Projection.h

@@ -430,6 +430,8 @@ class ProjectionPath {
 
   /// Given the SILType Base, expand every leaf nodes in the type tree.
   /// Include the intermediate nodes if OnlyLeafNode is false.
+  /// NOTE: this function returns a single empty projection path if the BaseType
+  /// is a leaf node in the type tree.
   static void expandTypeIntoLeafProjectionPaths(SILType BaseType,
                                                 SILModule *Mod,
                                                 ProjectionPathList &P,

lib/SIL/Projection.cpp

@@ -665,7 +665,7 @@ ProjectionPath::expandTypeIntoLeafProjectionPaths(SILType B, SILModule *Mod,
       continue;
     }
 
-    // This is NOT a leaf node, keep the intermediate nodes as well.
+    // If OnlyLeafNode is false, keep the intermediate nodes as well.
     if (!OnlyLeafNode)
       Paths.push_back(std::move(PP.getValue()));