Make build_sphinx work on missing apidoc

of course in that case there will be no API doc

doc/source/conf.py

@@ -13,10 +13,13 @@
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 
+from __future__ import print_function
 import sys
 import os
 import subprocess
 
+from sphinx.util.console import red
+
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
@@ -270,7 +273,6 @@ def run_apidoc(_):
     modules = ['larigira']
     exclude_files = [os.path.abspath(os.path.join(proj_dir, excl))
                      for excl in ('larigira/rpc.py', 'larigira/dbadmin/')]
-    for module in modules:
     output_path = os.path.join(cur_dir, 'api')
     cmd_path = 'sphinx-apidoc'
     if hasattr(sys, 'real_prefix'):  # Are we in a virtualenv?
@@ -278,6 +280,10 @@ def run_apidoc(_):
         cmd_path = os.path.abspath(os.path.join(sys.prefix,
                                                 'bin',
                                                 'sphinx-apidoc'))
+    if not os.path.exists(cmd_path):
+        print(red("No apidoc available!"), file=sys.stderr)
+        return
+    for module in modules:
         subprocess.check_call([cmd_path,
                                '--force',
                                '-o', output_path,