[ASTGen]: precondition that position is within buffer

Author: saehejkang

lib/ASTGen/Sources/ASTGen/Bridge.swift

@@ -32,13 +32,8 @@ extension BridgedSourceLoc {
     at position: AbsolutePosition,
     in buffer: UnsafeBufferPointer<UInt8>
   ) {
-    if let start = buffer.baseAddress,
-      position.utf8Offset >= 0 && position.utf8Offset < buffer.count {
-      assert(position.utf8Offset >= 0 && position.utf8Offset < buffer.count)
-      self = SourceLoc_advanced(BridgedSourceLoc(raw: start), SwiftInt(position.utf8Offset))
-    } else {
-      self = nil
-    }
+    precondition(position.utf8Offset >= 0 && position.utf8Offset < buffer.count)
+    self = SourceLoc_advanced(BridgedSourceLoc(raw: buffer.baseAddress), SwiftInt(position.utf8Offset))
   }
 }