Add fallback case in glGetShaderInfoLog

Some drivers do not always report the proper info log length
through glGetShaderiv which causes the JNI bindings to return
an empty log string. This change falls back to a length of
512 bytes when the queried length is 0. This is the same
fallback used in libhwui.

Bug: 16624915
Test: CtsOpenGLTestCases
Change-Id: I8deea6a7454efceb7c5d862b7055a34964f5bded