qb: fix config.params.sh parser break from 41dd469 + harden parser

Commit 41dd469 added a three-line '#' comment block above the new
HAVE_RETROARCH_PLAYLIST_MANAGER entry in qb/config.params.sh:

    # RetroArchPlaylistManager (iOS/tvOS playlist helper, also fine on
    # modern macOS).  Auto-disabled on pre-10.11 macOS targets by
    # config.libs.sh because the file uses Xcode 7-era Obj-C syntax.
    HAVE_RETROARCH_PLAYLIST_MANAGER=auto

which breaks configure with:

    qb/qb.params.sh: line 102: USER_#=auto: command not found

qb/config.params.sh is parsed line-by-line by parse_input() using
a plain 'while read -r VAR _' - '#' is not a comment introducer
in that loop, it's just the first whitespace-separated token of a
data line.  On each '#' line, VAR becomes '#', TMPVAR becomes '#',
NEWVAR becomes '#', and 'eval "USER_$NEWVAR=auto"' tries to run
'USER_#=auto' as a command.  The whole file's convention is inline
comments on HAVE_X=... lines only; no standalone '#' lines existed
before this one.

Two changes:

  qb/config.params.sh: fold the multi-line comment into a single
  inline '#' comment on the assignment line, matching the rest of
  the file.

  qb/qb.params.sh: harden parse_input() to skip blank lines and
  '#'-starting lines up front.  This doesn't change behaviour on
  today's well-formed file, but prevents the same foot-gun from
  biting anyone else who adds a comment block.

Author: LibretroAdmin

qb/config.params.sh

@@ -215,8 +215,5 @@ HAVE_GAME_AI=no
 HAVE_SMBCLIENT=auto        # SMB client support
 HAVE_BUILTINSMBCLIENT=no   # Use builtin libsmb2
 HAVE_COCOA=auto            # Cocoa support (Darwin/Apple)
-# RetroArchPlaylistManager (iOS/tvOS playlist helper, also fine on
-# modern macOS).  Auto-disabled on pre-10.11 macOS targets by
-# config.libs.sh because the file uses Xcode 7-era Obj-C syntax.
-HAVE_RETROARCH_PLAYLIST_MANAGER=auto
+HAVE_RETROARCH_PLAYLIST_MANAGER=auto # iOS/tvOS + macOS 10.11+ playlist helper (see qb/config.libs.sh)
 HAVE_MFI=auto              # GameController.framework joypad support (Apple)

qb/qb.params.sh

@@ -93,6 +93,13 @@ parse_input() # Parse stuff :V
 	config_opts='./configure'
 
 	while read -r VAR _; do
+		# Skip blank lines and comment-only lines.  Only HAVE_* or
+		# bare-name=VALUE assignments are meaningful here; anything
+		# else (like "# comment") would produce a broken eval such
+		# as 'USER_#=auto'.
+		case "$VAR" in
+			''|'#'*) continue ;;
+		esac
 		TMPVAR="${VAR%=*}"
 		NEWVAR="${TMPVAR##HAVE_}"
 		OPTS="${OPTS} $NEWVAR"