do not overwrite custom set module paths

Given that the module is now copied to the project directory
when no module path is set, we need the information that the
module path is empty. Therefore hand in the default module path
in a separate variable.

lib/lib.php

@@ -8,6 +8,7 @@ function loadSettings($sProjectDir)
     // set of settings.
     defined('CONST_DataDir') or define('CONST_DataDir', $_SERVER['NOMINATIM_DATADIR']);
     defined('CONST_BinDir') or define('CONST_BinDir', $_SERVER['NOMINATIM_BINDIR']);
+    defined('CONST_Default_ModulePath') or define('CONST_Default_ModulePath', $_SERVER['NOMINATIM_DATABASE_MODULE_SRC_PATH']);
 }
 
 function getSetting($sConfName, $sDefault = null)

lib/setup/SetupClass.php

@@ -148,7 +148,9 @@ class SetupFunctions
             // (aka we are running from the build dir).
             $sDest = CONST_InstallDir.'/module';
             if ($sDest != CONST_Default_ModulePath) {
-                mkdir($sDest);
+                if (!file_exists($sDest)) {
+                    mkdir($sDest);
+                }
                 if (!copy(CONST_Default_ModulePath.'/nominatim.so', $sDest.'/nominatim.so')) {
                     echo "Failed to copy database module to $sDest.";
                     exit(1);
@@ -158,6 +160,8 @@ class SetupFunctions
             } else {
                 info('Running from build directory. Leaving database module as is.');
             }
+        } else {
+            info('Using database module from DATABASE_MODULE_PATH ('.getSetting('DATABASE_MODULE_PATH').').');
         }
         // Try accessing the C module, so we know early if something is wrong
         $this->checkModulePresence(); // raises exception on failure