AK: Reduce code duplication in StringBuilder

Author: https://github.com/f-eiwu
Commit: 6da131d5db
Pull-request: https://github.com/SerenityOS/serenity/pull/1386
Reviewed-by: https://github.com/awesomekling

AK/StringBuilder.cpp

@@ -54,11 +54,7 @@ void StringBuilder::append(const StringView& str)
 
 void StringBuilder::append(const char* characters, size_t length)
 {
-    if (!length)
+    append(StringView { characters, length });
-        return;
-    will_append(length);
-    memcpy(m_buffer.data() + m_length, characters, length);
-    m_length += length;
 }
 
 void StringBuilder::append(char ch)