Revert "Foundation: fix missing string terminator"

This reverts commit f3a6f50.  It also
fixes the underlying issue of the heap corruption.

There is no guarantee that the underlying storage for an allocation is
done by `malloc`.  It is possible that the size may be small enough to
be pushed down to a stack allocation, which cannot be released by
`free`.  Buffers record how they are allocated and adjust the release
accordingly.  The safe way to release the memory is to use `deallocate`.

Although the initial approach fixed the heap corruption, it did so at
the single site, but this is a problem with a public interface.  Use the
`deallocate` method on the buffer when releasing the memory to ensure
that the correct mechanism is used for releasing the resources.

Thanks to Lily Vulcano for pressing me to investigate this further and
root cause the failure in the public interface!

Author: compnerd

Sources/Foundation/NSData.swift

@@ -599,12 +599,10 @@ open class NSData : NSObject, NSCopying, NSMutableCopying, NSSecureCoding {
 
         let capacity = estimateBase64Size(length: dataLength)
         let ptr = UnsafeMutableRawPointer.allocate(byteCount: capacity, alignment: 1)
-        defer { ptr.deallocate() }
         let buffer = UnsafeMutableRawBufferPointer(start: ptr, count: capacity)
         let length = NSData.base64EncodeBytes(self, options: options, buffer: buffer)
 
-        let utf8buffer = UnsafeBufferPointer<UInt8>(start: ptr.assumingMemoryBound(to: UInt8.self), count: length)
-        return String(decoding: utf8buffer, as: UTF8.self)
+        return String(bytesNoCopy: ptr, length: length, encoding: .ascii, freeWhenDone: true)!
     }
 
     /// Creates a Base64, UTF-8 encoded Data from the data object using the given options.

Sources/Foundation/NSString.swift

@@ -1359,7 +1359,7 @@ extension NSString {
         // just copy for now since the internal storage will be a copy anyhow
         self.init(bytes: bytes, length: len, encoding: encoding)
         if freeBuffer { // don't take the hint
-            free(bytes)
+          bytes.deallocate()
         }
     }