[LyX/2.1.x] Return an error if LaTeX is unable to compile the file. (cherry picked from commit 74ba63293becb647ddc2de95c320ce93d17f6068)

[Richard Heck]

commit 755b3131b0295060f39c96e886669f2d6621b9cf
Author: Richard Heck <rgh...@lyx.org>
Date:   Wed Mar 19 12:42:57 2014 -0400

    Return an error if LaTeX is unable to compile the file.
    (cherry picked from commit 74ba63293becb647ddc2de95c320ce93d17f6068)

diff --git a/lib/scripts/legacy_lyxpreview2ppm.py 
b/lib/scripts/legacy_lyxpreview2ppm.py
index fdc5a8e..d16e867 100644
--- a/lib/scripts/legacy_lyxpreview2ppm.py
+++ b/lib/scripts/legacy_lyxpreview2ppm.py
@@ -293,6 +293,8 @@ def legacy_conversion_step1(latex_file, dpi, output_format, 
fg_color, bg_color,
 
     # Compile the latex file.
     latex_status, latex_stdout = run_latex(latex, latex_file)
+    if latex_status:
+      return (latex_status, [])
 
     if pdf_output:
         return legacy_conversion_step3(latex_file, dpi, output_format, True, 
skipMetrics)
diff --git a/lib/scripts/lyxpreview2bitmap.py b/lib/scripts/lyxpreview2bitmap.py
index 4a2cddb..ace46d2 100755
--- a/lib/scripts/lyxpreview2bitmap.py
+++ b/lib/scripts/lyxpreview2bitmap.py
@@ -409,6 +409,8 @@ def main(argv):
 
     # Compile the latex file.
     latex_status, latex_stdout = run_latex(latex, latex_file, bibtex)
+    if latex_status:
+      return (latex_status, [])
 
     # The dvi output file name
     dvi_file = latex_file_re.sub(".dvi", latex_file)