[LyX/master] Fix another glitch with on-screen indentation.

[Enrico Forestieri]

commit a596736d76c318f94c36135756b1d1376c042539
Author: Enrico Forestieri <for...@lyx.org>
Date:   Thu May 22 23:47:38 2014 +0200

    Fix another glitch with on-screen indentation.
    
    If a new paragraph is created just before a nested environment,
    the indentation of the nested environment is not computed
    correctly because the parindent of the previous layout would
    also be erroneously taken into account. This would cause the
    nested environment to move back and forth when something is
    added to the new paragraph.

diff --git a/src/TextMetrics.cpp b/src/TextMetrics.cpp
index 226f842..de414ea 100644
--- a/src/TextMetrics.cpp
+++ b/src/TextMetrics.cpp
@@ -1896,6 +1896,13 @@ int TextMetrics::leftMargin(int max_width,
                if (newpar != pit_type(pars.size())) {
                        if (pars[newpar].layout().isEnvironment()) {
                                l_margin = leftMargin(max_width, newpar);
+                               // Remove the parindent that has been added
+                               // if the paragraph was empty.
+                               if (pars[newpar].empty()) {
+                                       docstring pi = 
pars[newpar].layout().parindent;
+                                       l_margin -= theFontMetrics(
+                                               
buffer.params().getFont()).signedWidth(pi);
+                               }
                        }
                        if (tclass.isDefaultLayout(par.layout())
                            || tclass.isPlainLayout(par.layout())) {