Fix documentation of numSelectorArgs.

Currently, the documentation for numSelectorArgs includes an incorrect
example. It shows a case where an argument of 1 will match a property
getter, but a getter will be matched only when N == 0.

This diff corrects the documentation and adds a test for numSelectorArgs(0).

Patch by Dave Lee.

llvm-svn: 246998
diff --git a/clang/unittests/ASTMatchers/ASTMatchersTest.cpp b/clang/unittests/ASTMatchers/ASTMatchersTest.cpp
index b443558..b0cd847 100644
--- a/clang/unittests/ASTMatchers/ASTMatchersTest.cpp
+++ b/clang/unittests/ASTMatchers/ASTMatchersTest.cpp
@@ -4890,6 +4890,9 @@
       objcMessageExpr(hasSelector("contents"), hasUnarySelector())));
   EXPECT_TRUE(matchesObjC(
       Objc1String,
+      objcMessageExpr(hasSelector("contents"), numSelectorArgs(0))));
+  EXPECT_TRUE(matchesObjC(
+      Objc1String,
       objcMessageExpr(matchesSelector("uppercase*"),
                       argumentCountIs(0)
                       )));