Security fixes for shellescaping

[arturxedex128]

There is no shellescaping in the plugin ... text elements could execute any command by enableing Images:

example:
<<img path="s';xeyes" height=5>>

patch is:

diff --git a/plugin/imager.vim b/plugin/imager.vim
index d4cdb0b..f92366f 100644
--- a/plugin/imager.vim
+++ b/plugin/imager.vim
@@ -334,14 +334,14 @@ function! s:GetWindowImages() " {{{1
                                else
                                        let snippet_string = formula
                                endif
-                               let hash = split(system(printf('echo -n "%s" | md5sum', snippet_string)), ' ')[0]
+                               let hash = split(system(printf('echo -n "%s" | md5sum', shellescape(snippet_string))), ' ')[0]

                                " Figure out what would be the directory and image paths
                                let dir_path = '/tmp/latex_images'
                                let image_path = dir_path . '/' . hash . '.png'

                                " Create the latex image if it doesn't already exist
-                               if !system('[ -e ' . "'" . image_path . "'" . ' ] && echo 1')
+                               if !system('[ -e ' . "'" . shellescape(image_path) . "'" . ' ] && echo 1')
                                        " If the foreground or background colors are a hex value, add HTML:
                                        " before them to make the hex code valid
                                        let foreground = g:imager#latex_foreground
@@ -363,8 +363,8 @@ function! s:GetWindowImages() " {{{1
                                        endif

                                        " Convert the latex expression into an image
-                                       silent! execute printf("!tex2im %s-b %s -t %s '%s'", preamble, background, foreground, formula)
-                                       silent! execute printf("!mv '%s/out.png' '%s'", getcwd(), image_path)
+                                       silent! execute printf("!tex2im %s-b %s -t %s '%s'", shellescape(preamble), background, foreground, shellescape(formula))
+                                       silent! execute printf("!mv '%s/out.png' '%s'", shellescape(getcwd()), shellescape(image_path))
                                endif
                                let new_image.path = image_path
                        endif
@@ -401,7 +401,7 @@ function! s:ShowImage(path, x, y, height) " {{{
        " Format the command to execute
        let g:imager#max_id += 1

-       let command = printf("bash %s '%s' %s %s %s", g:imager#ueberzug_path, a:path, a:x, a:y, a:height)
+       let command = printf("bash %s '%s' %s %s %s", g:imager#ueberzug_path, shellescape(a:path), shellescape(a:x), shellescape(a:y), shellescape(a:height))

        " Run the command in a terminal in a new tab, then close it
        new