[Utils] Remove the null buffer check, the crash was fixed

Fix: swiftlang#22417

Author: akyrtzi

Sources/SwiftSyntax/Utils.swift

@@ -71,8 +71,6 @@ public struct SourceEdit {
 
 extension String {
   static func fromBuffer(_ textBuffer: UnsafeBufferPointer<UInt8>) -> String {
-    // The string function crashes if the buffer is empty with nil pointer (SR-9869).
-    guard !textBuffer.isEmpty else { return String() }
     return String(decoding: textBuffer, as: UTF8.self)
   }