[LyX/master] Output debug message when creating bad length

[Jean-Marc Lasgouttes]

commit 5d29527916f74bcde767edf73dd9751775814b13
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Tue Mar 14 15:20:09 2017 +0100

    Output debug message when creating bad length
    
    Coverity is right to say that we should check the return value.
---
 src/Length.cpp |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/Length.cpp b/src/Length.cpp
index 62b7c84..3aa610f 100644
--- a/src/Length.cpp
+++ b/src/Length.cpp
@@ -21,6 +21,7 @@
 
 #include "frontends/FontMetrics.h"
 
+#include "support/debug.h"
 #include "support/docstream.h"
 #include "support/lstrings.h"
 #include "support/lyxlib.h"
@@ -362,9 +363,8 @@ GlueLength::GlueLength(Length const & len, Length const & 
plus,
 
 GlueLength::GlueLength(string const & data)
 {
-       // false positive from coverity
-       // coverity[CHECKED_RETURN]
-       isValidGlueLength(data, this);
+       if (!isValidGlueLength(data, this))
+               LYXERR0("Invalid glue length " + data);
 }