Polish
Protect against null CodeSource location

Update LogbackLoggingSystem to protect against a potential null
CodeSource result.

Fixes gh-2149
Merge branch '1.1.x'

Conflicts:
	spring-boot/src/main/java/org/springframework/boot/StartupInfoLogger.java
	spring-boot/src/main/java/org/springframework/boot/logging/logback/LogbackLoggingSystem.java