webui.sh: remove all `cd` related code

This may be helpful for
https://github.com/AUTOMATIC1111/stable-diffusion-webui/issues/7028,
because we won't change working directory to the repo now, instead,
we will use any working directory. If we set working directory to
a path contains repo and the custom --data-dir, the problem in this
issue should be solved.

Howewer, this may be treated as an incompatible change if some code
assume the working directory is always the repo.

Also, there may be another solution that always let --data-dir be the
subdirectory of the repo, but personally I think this may not be what
we actually need.

As this issue mainly influent on Docker and I am not familiar with
.bat files, updating webui.bat is skipped.

webui.sh: source env from repo instead $PWD

webui.sh

@@ -6,19 +6,18 @@
 
 # If run from macOS, load defaults from webui-macos-env.sh
 if [[ "$OSTYPE" == "darwin"* ]]; then
-    if [[ -f webui-macos-env.sh ]]
+    if [[ -f "$(dirname $0)/webui-macos-env.sh" ]]
         then
-        source ./webui-macos-env.sh
+        source "$(dirname $0)/webui-macos-env.sh"
     fi
 fi
 
 # Read variables from webui-user.sh
 # shellcheck source=/dev/null
-if [[ -f webui-user.sh ]]
+if [[ -f "$(dirname $0)/webui-user.sh" ]]
 then
-    source ./webui-user.sh
+    source "$(dirname $0)/webui-user.sh"
 fi
-
 # Set defaults
 # Install directory without trailing slash
 if [[ -z "${install_dir}" ]]
@@ -47,12 +46,12 @@ fi
 # python3 venv without trailing slash (defaults to ${install_dir}/${clone_dir}/venv)
 if [[ -z "${venv_dir}" ]]
 then
-    venv_dir="venv"
+    venv_dir="${install_dir}/${clone_dir}/venv"
 fi
 
 if [[ -z "${LAUNCH_SCRIPT}" ]]
 then
-    LAUNCH_SCRIPT="launch.py"
+    LAUNCH_SCRIPT="${install_dir}/${clone_dir}/launch.py"
 fi
 
 # this script cannot be run as root by default
@@ -140,22 +139,23 @@ then
     exit 1
 fi
 
-cd "${install_dir}"/ || { printf "\e[1m\e[31mERROR: Can't cd to %s/, aborting...\e[0m" "${install_dir}"; exit 1; }
-if [[ -d "${clone_dir}" ]]
+if [[ ! -d "${install_dir}/${clone_dir}" ]]
 then
-    cd "${clone_dir}"/ || { printf "\e[1m\e[31mERROR: Can't cd to %s/%s/, aborting...\e[0m" "${install_dir}" "${clone_dir}"; exit 1; }
-else
     printf "\n%s\n" "${delimiter}"
     printf "Clone stable-diffusion-webui"
     printf "\n%s\n" "${delimiter}"
-    "${GIT}" clone https://github.com/AUTOMATIC1111/stable-diffusion-webui.git "${clone_dir}"
-    cd "${clone_dir}"/ || { printf "\e[1m\e[31mERROR: Can't cd to %s/%s/, aborting...\e[0m" "${install_dir}" "${clone_dir}"; exit 1; }
+    mkdir -p "${install_dir}"
+    "${GIT}" clone https://github.com/AUTOMATIC1111/stable-diffusion-webui.git "${install_dir}/${clone_dir}"
 fi
 
 printf "\n%s\n" "${delimiter}"
 printf "Create and activate python venv"
 printf "\n%s\n" "${delimiter}"
-cd "${install_dir}"/"${clone_dir}"/ || { printf "\e[1m\e[31mERROR: Can't cd to %s/%s/, aborting...\e[0m" "${install_dir}" "${clone_dir}"; exit 1; }
+# Make venv_dir absolute
+if [[ "${venv_dir}" != /* ]]
+then
+    venv_dir="${install_dir}/${clone_dir}/${venv_dir}"
+fi
 if [[ ! -d "${venv_dir}" ]]
 then
     "${python_cmd}" -m venv "${venv_dir}"