Add isValid() call to QJniEnvironment

Task-number: QTBUG-92952
Change-Id: I3bce2881c10a8bfcc8771002a3349644c6f05cb3
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

src/corelib/kernel/qjnienvironment.cpp

@@ -137,6 +137,16 @@ QJniEnvironment::~QJniEnvironment()
     checkAndClearExceptions();
 }
 
+/*!
+    Returns \c true if this instance holds a valid JNIEnv object.
+
+    \since 6.2
+*/
+bool QJniEnvironment::isValid() const
+{
+    return d->jniEnv;
+}
+
 /*!
     \fn JNIEnv *QJniEnvironment::operator->() const
 

src/corelib/kernel/qjnienvironment.h

@@ -54,6 +54,7 @@ class Q_CORE_EXPORT QJniEnvironment
 public:
     QJniEnvironment();
     ~QJniEnvironment();
+    bool isValid() const;
     JNIEnv *operator->() const;
     JNIEnv &operator*() const;
     JNIEnv *jniEnv() const;