Fix '-Wclazy-qstring-left' warning
Fix '-Wclazy-qstring-left' warning

The warning says 'Use QString::at(0) instead of QString::left(1) to
avoid temporary allocations (just be sure the string isn't empty).'

Change-Id: I4ef427c4a60e7f9e40a16b3e8b64ea13e167f1ee
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@qt.io>

qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs