Update paintutils.lua

Resolve a few potential bugs.

src/main/resources/assets/computercraft/lua/rom/apis/paintutils.lua

@@ -1,5 +1,15 @@
 local setPos, write, setCol, blit = term.setCursorPos, term.write, term.setBackgroundColour, term.blit
 
+local maxn = table.maxn or function( tTable )
+    local maxn = 0
+    for n in pairs( tTable ) do
+        if type( n ) == "number" and n > max then
+            maxn = n
+        end
+    end
+    return maxn
+end
+
 local tColourLookup = {}
 for n=1,16 do
     tColourLookup[ string.sub( "0123456789abcdef",n,n ) ] = 2^(n-1)
@@ -33,15 +43,22 @@ function saveImage( tImage, sPath )
     end
 
     local file = fs.open(sPath, "w" )
+    if not file then return false end
     
-    for y=1,#tImage do
-        local tOld, tNew = tImage[y], {}
-        for x=1,#tOld do
-            tNew[x] = tColourLookup[ tOld[x] ] or " "
-        end
-        file.writeLine( table.concat( tNew ) )
+    for y=1,maxn( tImage ) do
+        local tOld, tNew, last = tImage[y], {}, 0
+        if tOld then for x=1,maxn( tOld ) do
+            local thisCol = tColourLookup[ tOld[x] ]
+            if thisCol then
+                tNew[x], last = thisCol, x
+            else
+                tNew[x] = " "
+            end
+        end end
+        file.writeLine( table.concat( tNew, "", 1, last ) )
     end
     file.close()
+    return true
 end
 
 function drawPixel( xPos, yPos, nColour )
@@ -93,9 +110,8 @@ function drawLine( startX, startY, endX, endY, nColour )
     local yDiff = maxY - minY
     
     if minY == maxY then
-        local sStr = string.rep( " ", xDiff + 1 )
         setPos( minX, minY )
-        write( sStr )
+        write( string.rep( " ", xDiff + 1 ) )
         return
     end
             
@@ -193,9 +209,9 @@ function drawImage( tImage, xPos, yPos )
     if type( tImage ) ~= "table" or type( xPos ) ~= "number" or type( yPos ) ~= "number" then
         error( "Expected image, x, y", 2 )
     end
-    for y=1,#tImage do
+    for y=1,maxn( tImage ) do
         local tLine, sBG, counter = tImage[y], {}, 0
-        for x=1,#tLine+1 do
+        if tLine then for x=1,maxn( tLine )+1 do
             local px = tLine[x] or 0
             if px > 0 then
                 counter = counter + 1
@@ -206,6 +222,6 @@ function drawImage( tImage, xPos, yPos )
                 blit( sT, sT, table.concat( sBG ) )
                 sBG, counter = {}, 0
             end
-        end
+        end end
     end
 end