[LyX/master] Use getArg to read math-extern arguments

[Jean-Marc Lasgouttes]

commit 2d02c39d565901d91f3cc400d9642ff6e9a134d8
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Tue Jun 5 11:24:05 2018 +0200

    Use getArg to read math-extern arguments
    
    This avoids a use of istringstream that coverity dislikes.
---
 src/mathed/InsetMathHull.cpp |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/src/mathed/InsetMathHull.cpp b/src/mathed/InsetMathHull.cpp
index ff7595f..61d078a 100644
--- a/src/mathed/InsetMathHull.cpp
+++ b/src/mathed/InsetMathHull.cpp
@@ -1722,13 +1722,11 @@ void InsetMathHull::check() const
 
 void InsetMathHull::doExtern(Cursor & cur, FuncRequest & func)
 {
-       docstring dlang;
-       docstring extra;
-       idocstringstream iss(func.argument());
-       iss >> dlang >> extra;
+       //FIXME: sort out whether we want std::string or docstring for those
+       string const lang = func.getArg(0);
+       docstring extra = from_utf8(func.getArg(1));
        if (extra.empty())
                extra = from_ascii("noextra");
-       string const lang = to_ascii(dlang);
 
        // replace selection with result of computation
        if (reduceSelectionToOneCell(cur)) {