Fix finding message template in linux dev build

indra/newview/llstartup.cpp

@@ -528,6 +528,15 @@ bool idle_startup()
                 message_template_path = gDirUtilp->getExpandedFilename(LL_PATH_EXECUTABLE, "app_settings", "message_template.msg");
                 found_template = LLFile::fopen(message_template_path, "r");     /* Flawfinder: ignore */
             }
+        #elif LL_LINUX
+            // On the linux dev builds, unpackaged, the message_template.msg
+            // file will be located in:
+            // build-linux**/newview/packaged/app_settings
+            if (!found_template)
+            {
+                message_template_path = gDirUtilp->getExpandedFilename(LL_PATH_EXECUTABLE, "..", "app_settings", "message_template.msg");
+                found_template = LLFile::fopen(message_template_path, "r");     /* Flawfinder: ignore */
+            }
         #elif LL_DARWIN
             // On Mac dev builds, message_template.msg lives in:
             // indra/build-*/newview/<config>/Second Life/Contents/Resources/app_settings