Change template parameter to disambiguate call to QLatin1String constructor

Summary:
Qt 5.10 added a new constructor overload which made the call to QLatin1String
constructor with size_t as second parameter ambigious.

Reviewers: #swift_pilot_client, msutcliffe

Reviewed By: #swift_pilot_client, msutcliffe

Subscribers: jenkins

Differential Revision: https://dev.swift-project.org/D47

src/blackmisc/pq/measurementunit.h

@@ -227,7 +227,7 @@ namespace BlackMisc
             };
 
             //! Workaround to constant-initialize QLatin1String on platforms without constexpr strlen.
-            template <size_t N>
+            template <int N>
             static Q_DECL_CONSTEXPR QLatin1String constQLatin1(const char (&str)[N])
             {
                 return QLatin1String(str, N - 1); // -1 because N includes the null terminator