bug#18826: 24.3.94; c++-mode bad indentation after programmatic insert with locally changed syntax table

[Dmitry Gutov <dgutov@yandex.ru>]

I think the following should be harmless. Why does it result in broken
indentation?

1. Open in c++-mode buffer with following contents:

int main(int argc, char** argv) {
  fgets(0, 1, 2);
}

2. Add an empty line after the semicolon, move cursor there, and
evaluate this:

(with-syntax-table (make-char-table 'syntax-table nil)
  (modify-syntax-entry ?\( "(")
  (modify-syntax-entry ?\) ")")
  (modify-syntax-entry ?< "(")
  (modify-syntax-entry ?> ")")
  (insert "fgets(0, 1, 2)"))

3. Press `;', see the indentation of the current line change, and
include (erroneously) two extra spaces:

int main(int argc, char** argv) {
  fgets(0, 1, 2);
    fgets(0, 1, 2);
}

Originally: https://github.com/company-mode/company-mode/issues/212

In GNU Emacs 24.3.94.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.8)
 of 2014-10-06 on axl
Repository revision: 117555 sdl.web@gmail.com-20141005005838-oyl694hqhu2d3632
Windowing system distributor `The X.Org Foundation', version 11.0.11501000
System Description:	Ubuntu 14.04.1 LTS