Warning: Illegal string offset in PHP 5.4 [duplicate]

Answer 1

You need to make sure, that $meta is actually of type array. The warning explicitly tells you, that $meta seems to be a string and not an array

Illegal string offset
        ^^^^^^

To avoid this error you may also check for the needed fields

for($i = 0; $i < 3; $i++) {
    if ( !is_array($meta) || !array_key_exists('quote'. ($i+1), $meta) ){
         continue;
    }
    // your code
}

Answer 2

If $meta is null whenever there's no data to process:

if( !is_null($meta) ){
    for($i = 0; $i < 3; $i++) {
        // ...
    }
}

You should be able to do more checks if necessary. That depends on what that get_post_meta() function is designed to return.