build-pkg, second pass: fix fail on broken package

If a package is found to be broken on the first pass, then
prev_files = nil, because this structure is filled only
for non-broken packages.

See https://github.com/mxe/mxe/pull/1243#issuecomment-211137555

1 files changed, 8 insertions, 6 deletions

diff --git a/tools/build-pkg.lua b/tools/build-pkg.lua
index 56b1aaa..0af1d33 100755
--- a/tools/build-pkg.lua
+++ b/tools/build-pkg.lua
@@ -602,13 +602,15 @@ local function prepareTree(pass, item, item2deps, prev_files, item2index)
             item2index,
             'first'
         )
-        -- Remove files of item from previous build.
-        for _, file in ipairs(prev_files) do
-            os.remove(file)
-        end
         removeEmptyDirs()
-        gitAdd()
-        gitCommit(("Remove %s to rebuild it"):format(item, pass))
+        if prev_files then
+            -- Remove files of item from previous build.
+            for _, file in ipairs(prev_files) do
+                os.remove(file)
+            end
+            gitAdd()
+            gitCommit(("Remove %s to rebuild it"):format(item, pass))
+        end
     else
         error("Unknown pass: " .. pass)
     end