Don't throw in socket_read if socket_read_all returns < 0.

All codepaths in socket_read_all that return a negative value have
already thrown an exception. socket_read should not throw again.

This causes debuggagle apps to crash with a JNI failure if
LocalSocket#read gets an error.

Test: atest CtsNetTestCases
Bug: 229813087
Change-Id: I2a04a799d3748c221f8555fa7afc40d73f0f392c