SI-9268 Be robust against absent classfiles during signature parsing

When parsing a Java generic signature that references an inner
class `A$B`, we were tripping an assertion if the enclosing class
`A` was absent.

This commit creates a stub symbol for `B` when this happens, rather
than continuing on with `NoSymbol`.

The enclosed test shows that we can instantiate a class containing
a method referring to such an inner class with only a warning
about the absent classfile, and that an error is issued only upon
a subsequent attempt to call the method.

1 files changed, 5 insertions, 0 deletions

diff --git a/test/files/run/t9268.check b/test/files/run/t9268.check
new file mode 100644
index 0000000000..90ef940eb3
--- /dev/null
+++ b/test/files/run/t9268.check
@@ -0,0 +1,5 @@
+Compiling Client1
+pos: NoPosition Class Waiter not found - continuing with a stub. WARNING
+Compiling Client2
+pos: NoPosition Class Waiter not found - continuing with a stub. WARNING
+pos: NoPosition Unable to locate class corresponding to inner class entry for Predicate in owner Waiter ERROR