bugfix: awk scripts fail without local data

src/awk/artists.awk

@@ -2,9 +2,11 @@ BEGIN {
   OFS="\t"
   local_artists[0] = 0
   delete local_artists[0]
-  while ((getline < file_local_artists) == 1) 
-    local_artists[$1] = 1
-  close(file_local_artists)
+  if (file_local_artists) {
+    while ((getline < file_local_artists) == 1)
+      local_artists[$1] = 1
+    close(file_local_artists)
+  }
 }
 { 
   gsub("&", "\\\\&")

src/awk/releasegroups.awk

@@ -2,9 +2,11 @@ BEGIN {
   OFS="\t"
   local_releasegroups[0] = 0
   delete local_releasegroups[0]
-  while ((getline < file_local_releasegroups) == 1) 
-    local_releasegroups[$1] = 1
-  close(file_local_releasegroups)
+  if (file_local_releasegroups) {
+    while ((getline < file_local_releasegroups) == 1)
+      local_releasegroups[$1] = 1
+    close(file_local_releasegroups)
+  }
 }
 {
   line_type=""

src/awk/releases.awk

@@ -2,9 +2,11 @@ BEGIN {
   OFS="\t"
   local_releases[0] = 0
   delete local_releases[0]
-  while ((getline < file_local_releases) == 1) 
-    local_releases[$1] = 1
-  close(file_local_releases)
+  if (file_local_releases) {
+    while ((getline < file_local_releases) == 1)
+      local_releases[$1] = 1
+    close(file_local_releases)
+  }
 }
 {
   id = $1