[LyX/master] Avoid endless loop when the window is too narrow

[Jean-Marc Lasgouttes]

commit 8009edd3d4f3deee5ed8721113bbf31abe9e0aa6
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Wed Mar 2 23:59:40 2016 +0100

    Avoid endless loop when the window is too narrow
    
     * breakRow: remove wrong condition that would silently eat the contents of 
the
       paragraph when the window is narrower than left margin
    
     * breakRow: make sure that there is at least one element in each row
    
     * breakAt: when force-breaking a row element, make sure it is not empty. 
Doing
       so may create empty rows and therefore a endless loop.
    
    Fixes bugs #9962 and #10001.

diff --git a/src/TextMetrics.cpp b/src/TextMetrics.cpp
index cb1c4bd..f37e678 100644
--- a/src/TextMetrics.cpp
+++ b/src/TextMetrics.cpp
@@ -803,7 +803,7 @@ void TextMetrics::breakRow(Row & row, int const 
right_margin, pit_type const pit
        // the width available for the row.
        int const width = max_width_ - row.right_margin;
 
-       if (pos >= end || row.width() > width) {
+       if (pos >= end) {
                row.endpos(end);
                return;
        }
@@ -828,7 +828,7 @@ void TextMetrics::breakRow(Row & row, int const 
right_margin, pit_type const pit
        // or the end of the par, then build a representation of the row.
        pos_type i = pos;
        FontIterator fi = FontIterator(*this, par, pit, pos);
-       while (i < end && row.width() <= width) {
+       do {
                char_type c = par.getChar(i);
                // The most special cases are handled first.
                if (par.isInset(i)) {
@@ -893,7 +893,7 @@ void TextMetrics::breakRow(Row & row, int const 
right_margin, pit_type const pit
 
                ++i;
                ++fi;
-       }
+       } while (i < end && row.width() <= width);
        row.finalizeLast();
        row.endpos(i);
 
diff --git a/src/frontends/qt4/GuiFontMetrics.cpp 
b/src/frontends/qt4/GuiFontMetrics.cpp
index fdb8c73..eade8cc 100644
--- a/src/frontends/qt4/GuiFontMetrics.cpp
+++ b/src/frontends/qt4/GuiFontMetrics.cpp
@@ -240,7 +240,7 @@ bool GuiFontMetrics::breakAt(docstring & s, int & x, bool 
const rtl, bool const
        line.setLineWidth(x);
        tl.createLine();
        tl.endLayout();
-       if (int(line.naturalTextWidth()) > x)
+       if ((force && line.textLength() == 1) || int(line.naturalTextWidth()) > 
x)
                return false;
        x = int(line.naturalTextWidth());
        // The -1 is here to account for the leading zerow_nbsp.