Handle Flutter SDK paths with spaces in doctor (#6578)

bin/flutter

@@ -47,7 +47,7 @@ DART="$DART_SDK_PATH/bin/dart"
     "$DART" --snapshot="$SNAPSHOT_PATH" --packages="$FLUTTER_TOOLS_DIR/.packages" "$SCRIPT_PATH"
     echo $REVISION > "$STAMP_PATH"
   fi
-) 3< $PROG_NAME
+) 3< "$PROG_NAME"
 
 set +e
 "$DART" "$SNAPSHOT_PATH" "$@"

bin/internal/update_dart_sdk.sh

@@ -5,7 +5,7 @@
 
 set -e
 
-FLUTTER_ROOT=$(dirname $(dirname $(dirname "${BASH_SOURCE[0]}")))
+FLUTTER_ROOT="$(dirname "$(dirname "$(dirname "${BASH_SOURCE[0]}")")")"
 
 DART_SDK_PATH="$FLUTTER_ROOT/bin/cache/dart-sdk"
 DART_SDK_STAMP_PATH="$FLUTTER_ROOT/bin/cache/dart-sdk.stamp"