Add a test for trying to construct a Data from an invalid NSString, and fix existing invalid NSString construction

Author: Catfish-Man

test/stdlib/Inputs/FoundationBridge/FoundationBridge.h

@@ -86,12 +86,12 @@ static inline BOOL NSStringBridgeTestEqual(NSString * _Nonnull a, NSString * _No
 }
 
 static inline NSString *getNSStringWithUnpairedSurrogate() {
-  unichar chars[16] = {
+  unichar chars[19] = {
     0x0020, 0x0020, 0x0020, 0x0020, 0x0020, 0x0020,
     0x0020, 0x0020, 0x0020, 0x0020, 0x0020, 0x0020,
     0x0020, 0x0020, 0x0020, 0x0020, 0x0020, 0x0020,
     0xD800 };
-  return [NSString stringWithCharacters:chars length:1];
+  return [NSString stringWithCharacters:chars length:19];
 }
 
 NS_ASSUME_NONNULL_END

test/stdlib/TestNSString.swift

@@ -60,6 +60,7 @@ class TestNSString : TestNSStringSuper {
   func test_unpairedSurrogates() {
     let evil = getNSStringWithUnpairedSurrogate();
     print("\(evil)")
+    print(evil.data(using: .utf8))
   }
 
 }