Fix git capsule fallback when __git_ps1 is empty

.context.json

@@ -432,6 +432,6 @@
     "On macOS, installer is per-user and sources from .bashrc/.bash_profile.",
     "Seasonal palettes and contest pack are now documented directly in main.",
     "README uses images/bash-pallete.png.",
-    "Git capsule prefers __git_ps1 and falls back to git symbolic-ref/short hash when git-prompt is unavailable."
+    "Git capsule prefers __git_ps1 and falls back to git symbolic-ref/short hash when git-prompt is unavailable or returns empty."
   ]
 }

dotfiles/ps1/ps1.sh

@@ -169,7 +169,11 @@ __git_capsule() {
   if declare -F __git_ps1 >/dev/null 2>&1; then
     has_ps1=1
     info="$(__git_ps1 "%s" 2>/dev/null)"
-  else
+    if [[ -z "$info" ]]; then
+      has_ps1=0
+    fi
+  fi
+  if [[ -z "$info" ]]; then
     if command -v git >/dev/null 2>&1; then
       info="$(git symbolic-ref --quiet --short HEAD 2>/dev/null || git rev-parse --short HEAD 2>/dev/null)"
     fi