[Fix] install.sh: start a new line before appending to a profile that does not end with one

Fixes #3951

install.sh

@@ -490,6 +490,9 @@ nvm_do_install() {
     # shellcheck disable=SC2016
     if ${BASH_OR_ZSH} && ! command grep -qc '$NVM_DIR/bash_completion' "$NVM_PROFILE"; then
       nvm_echo "=> Appending bash_completion source string to $NVM_PROFILE"
+      if [ -n "$(command tail -c 1 "$NVM_PROFILE")" ]; then
+        nvm_echo >> "$NVM_PROFILE"
+      fi
       command printf '%b' "$COMPLETION_STR" >> "$NVM_PROFILE"
     else
       nvm_echo "=> bash_completion source string already in ${NVM_PROFILE}"