title: clang-format reflowing comments incorrectly and is non repeatable
body: <p>The following code snippet in C++, when formatted using <code>clang-format-8</code>, gives incorrect result in the first run (disrespecting <code>ColumnWidth=80</code>) and correct result in the second and subsequent runs. Note: the code contains tab in the comments (something which was not indented using spaces, as they were mere comments). It seems <code>ReflowComments</code> is not working as intended. Why is it so and how to handle such cases, especially when we need to reflow long comments and merge changes across previously formatted code in different <code>git</code> branch.</p>
  <p><code>clang-format-8 -style=Google -i src/test.cpp</code></p>
  <pre><code>void f() {
    // arg0,
    // arg1,                                              arg2,                                               arg3,                                               arg4,
    //                                                arg5,
    //                                                arg6,
    //                                                arg7,
    //                                                arg8,
    //                                                arg9,
    //                                                arg10
  }
  </code></pre>
  <p>Formatted Version 1 (Incorrect)</p>
  <pre><code>void f() {
    // arg0,
    // arg1,                                              arg2,
    // arg3,
    // arg4,                                              arg5,                                               arg6,                                               arg7,                                               arg8,                                               arg9,                                               arg10
  }
  </code></pre>
  <p>Formatted Version 2 (Not incorrect)</p>
  <pre><code>void f() {
    // arg0,
    // arg1,
    // arg2, arg3, arg4,
    // arg5,                                              arg6,
    // arg7,                                              arg8,
    // arg9,
    // arg10
  }
  </code></pre>