KPath: Prevent setting a KPath to itself causing use-after-free.

SetTo frees the buffer before setting it to the new one,
but if KPath sets itself to ... itself, then it will of course
try to access the buffer again.

Spotted by clang-analyzer (amidst quite a few false positives,
so this doesn't seem like an especially good rabbit hole
to go down right now.)

src/system/kernel/fs/KPath.cpp

@@ -356,6 +356,9 @@ KPath::Normalize(bool traverseLeafLink)
 KPath&
 KPath::operator=(const KPath& other)
 {
+	if (other.fBuffer == fBuffer)
+		return *this;
+
 	SetTo(other.fBuffer, fLazy ? KPath::LAZY_ALLOC : KPath::DEFAULT,
 		other.fBufferSize);
 	return *this;