Unix: fall back to English when a language file is unusable

An empty language file made VeraCrypt access the first element of an
empty vector, and any language file without a language element crashed
it at startup, when LanguageStrings::Init took the first element of an
empty node list. A file with an unterminated tag made initialization
fail instead, so VeraCrypt could not start until the preferences file
was edited. Read the file only if it is not empty, and ignore a
language file that cannot be parsed or has no language element, keeping
the built-in English strings.

Also fall back when the optional language file cannot be opened or
read completely. Catch I/O failures at the resource loader, leaving
preference-loading errors outside the handler.

src/Main/LanguageStrings.cpp

@@ -57,14 +57,30 @@ namespace VeraCrypt
 		}
 
 		string translatedXml = Resources::GetLanguageXml(PreferredLang);
-		foreach (XmlNode node, XmlParser (translatedXml).GetNodes (L"entry"))
+		XmlNodeList translatedEntries, languageNodes;
+		try
+		{
+			translatedEntries = XmlParser (translatedXml).GetNodes (L"entry");
+			languageNodes = XmlParser (translatedXml).GetNodes (L"language");
+		}
+		catch (ParameterIncorrect&) { }
+
+		// Keep the built-in strings if the language file is empty, malformed or has no language element
+		if (languageNodes.empty())
+		{
+			translatedEntries.clear();
+			languageNodes = XmlParser (def).GetNodes (L"language");
+			PreferredLang = "en";
+		}
+
+		foreach (XmlNode node, translatedEntries)
 		{
 			wxString text = node.InnerText;
 			text.Replace (L"\\n", L"\n");
 			Map[StringConverter::ToSingle (wstring (node.Attributes[L"key"]))] = text;
 		}
 
-		XmlNode node = XmlParser (translatedXml).GetNodes (L"language").front();
+		XmlNode node = languageNodes.front();
 		Map["LANGUAGE_TRANSLATORS"] = wxString (node.Attributes[L"translators"]);
 		Map["CURRENT_LANGUAGE_PACK"] = wxString (node.Attributes[L"name"]);
 	}

src/Main/Resources.cpp

@@ -149,14 +149,24 @@ namespace VeraCrypt
 		}
 		FilesystemPath xml(filename);
 		if ( xml.IsFile() ){
-			File file;
-			file.Open (xml, File::OpenRead, File::ShareRead);
-			vector <uint8> keyfileData (file.Length());
-			BufferPtr keyfileDataBuf (&keyfileData.front(), keyfileData.size());
-			file.ReadCompleteBuffer (keyfileDataBuf);
-			file.Close();
-			string langxml(keyfileData.begin(), keyfileData.end());
-			return langxml;
+			try
+			{
+				File file;
+				file.Open (xml, File::OpenRead, File::ShareRead);
+				vector <uint8> keyfileData (file.Length());
+				if (!keyfileData.empty())
+				{
+					BufferPtr keyfileDataBuf (&keyfileData.front(), keyfileData.size());
+					file.ReadCompleteBuffer (keyfileDataBuf);
+				}
+				file.Close();
+				string langxml(keyfileData.begin(), keyfileData.end());
+				return langxml;
+			}
+			// An optional translation must not prevent startup if it cannot be
+			// opened or read completely (for example, if it shrinks while reading).
+			catch (SystemException&) { }
+			catch (InsufficientData&) { }
 		}
 		static uint8 LanguageXml[] =
 		{