fix nvm assumption

recipes/build.sh

@@ -1,7 +1,14 @@
 #!/bin/bash
 set -e
 
+
+
 # check and install dependencies
+if ! command -v pip3 &> /dev/null; then
+    sudo apt update
+    sudo apt install -y python3-pip
+fi
+
 if ! pip3 show jsonschema &> /dev/null; then
     pip3 install jsonschema
 fi
@@ -15,16 +22,20 @@ if ! command -v 7z &> /dev/null; then
 fi
 
 if ! command -v mdpdf &> /dev/null; then
-    export NVM_DIR="$HOME/.nvm"
-    [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"  # This loads nvm
 
-    if ! command -v mdpdf &> /dev/null; then
-        curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.3/install.sh | bash
-        source ~/.bashrc
-        nvm list-remote
-        nvm install v22.3.0
-        nvm list
-        npm install mdpdf -g
+    # check if directory $HOME/.nvm exists:
+    if [ ! -d "$HOME/.nvm" ]; then
+        if ! command -v mdpdf &> /dev/null; then
+            curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.3/install.sh | bash
+            source ~/.bashrc
+            nvm list-remote
+            nvm install v22.3.0
+            nvm list
+            npm install mdpdf -g
+        fi
+    else
+        export NVM_DIR="$HOME/.nvm"
+        [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"  # This loads nvm
     fi
 fi