Style tweak and an extra comment.

Change _swift_initRootPath() to do an early return, which reduces indentation.

Add a comment to reinforce that we can't use GetFinalPathNameByHandle() in
_swift_initRuntimePath().

rdar://103071801

Author: al45tair

stdlib/public/runtime/Paths.cpp

@@ -244,22 +244,24 @@ _swift_initRootPath(void *)
 {
   // SWIFT_ROOT overrides the path returned by this function
   const char *swiftRoot = swift::runtime::environment::SWIFT_ROOT();
-  if (swiftRoot && *swiftRoot) {
-    size_t len = std::strlen(swiftRoot);
 
-    // Ensure that there's a trailing slash
-    if (_swift_isPathSep(swiftRoot[len - 1])) {
-      rootPath = swiftRoot;
-    } else {
-      char *thePath = (char *)malloc(len + 2);
-      std::memcpy(thePath, swiftRoot, len);
-      thePath[len] = PATHSEP_CHR;
-      thePath[len + 1] = 0;
+  if (!swiftRoot || !*swiftRoot) {
+    rootPath = _swift_getDefaultRootPath();
+    return;
+  }
 
-      rootPath = thePath;
-    }
+  size_t len = std::strlen(swiftRoot);
+
+  // Ensure that there's a trailing slash
+  if (_swift_isPathSep(swiftRoot[len - 1])) {
+    rootPath = swiftRoot;
   } else {
-    rootPath = _swift_getDefaultRootPath();
+    char *thePath = (char *)malloc(len + 2);
+    std::memcpy(thePath, swiftRoot, len);
+    thePath[len] = PATHSEP_CHR;
+    thePath[len + 1] = 0;
+
+    rootPath = thePath;
   }
 }
 
@@ -479,6 +481,9 @@ _swift_initRuntimePath(void *) {
   const DWORD dwBufSize = 4096;
   LPWSTR lpFilename = (LPWSTR)std::malloc(dwBufSize * sizeof(WCHAR));
 
+  // Again, we can't use GetFinalPathNameByHandle for the reasons given
+  // above.
+
   DWORD dwRet = GetMappedFileNameW(GetCurrentProcess(),
                                    (void *)_swift_initRuntimePath,
                                    lpFilename,