OlmAccount methods trigger an exception when they fail.

...k/src/androidTest/java/org/matrix/olm/OlmAccountTest.java

...k/src/androidTest/java/org/matrix/olm/OlmSessionTest.java

...k/src/androidTest/java/org/matrix/olm/OlmUtilityTest.java

...bSdk/olm-sdk/src/main/java/org/matrix/olm/OlmAccount.java

...dk/olm-sdk/src/main/java/org/matrix/olm/OlmException.java

java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.cpp

java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.h

java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_jni.h