qdoc: Fix crash on ClangCodeParser::getMoreArgs()

ASSERT failure in QList<T>::at: "index out of range" for documentation
modules that do not have any headers.

Change-Id: Ia8bc776d9c48c34b962356a65f74b2c7fe1d2d8c
Reviewed-by: Martin Smith <martin.smith@qt.io>

1 files changed, 4 insertions, 3 deletions

diff --git a/src/qdoc/clangcodeparser.cpp b/src/qdoc/clangcodeparser.cpp
index 44da9d7ed..e6c6d5801 100644
--- a/src/qdoc/clangcodeparser.cpp
+++ b/src/qdoc/clangcodeparser.cpp
@@ -1057,14 +1057,15 @@ void ClangCodeParser::getMoreArgs()
           that list instead.
          */
         QList<QString> headers = allHeaders_.values();
-        QString filePath = headers.at(0);
         auto forest = qdb_->searchOrder();
 
         QByteArray version = qdb_->version().toUtf8();
         QString basicIncludeDir = QDir::cleanPath(QString(Config::installDir + "/../include"));
         moreArgs_ += "-I" + basicIncludeDir.toLatin1();
-        moreArgs_ += "-I" + QDir::cleanPath(QString(filePath + "/../")).toLatin1();
-        moreArgs_ += "-I" + QDir::cleanPath(QString(filePath + "/../../")).toLatin1();
+        if (!headers.isEmpty()) {
+            moreArgs_ += "-I" + QDir::cleanPath(QString(headers.at(0) + "/../")).toLatin1();
+            moreArgs_ += "-I" + QDir::cleanPath(QString(headers.at(0) + "/../../")).toLatin1();
+        }
         for (const auto &s : forest) {
             QString module = basicIncludeDir +"/" + s->camelCaseModuleName();
             moreArgs_ += QString("-I" + module).toLatin1();