AK: Rename error() to has_error() for streams.

Author: https://github.com/asynts
Commit: bc332aca33
Pull-request: https://github.com/SerenityOS/serenity/pull/3220
Reviewed-by: https://github.com/awesomekling

AK/Stream.h

@@ -37,10 +37,10 @@ class Stream {
 public:
     virtual ~Stream()
     {
-        ASSERT(!error());
+        ASSERT(!has_error());
     }
 
-    bool error() const { return m_error; }
+    bool has_error() const { return m_error; }
 
     bool handle_error() { return exchange(m_error, false); }