Fix parsing of GPL files

Can you tell this was *not* tested whatsoever?

src/gfx/pal_spec.cpp

@@ -352,24 +352,30 @@ static void parseGPLFile(std::filebuf &file) {
 	}
 
 	uint16_t nbColors = 0;
-	uint16_t maxNbColors = options.nbColorsPerPal * options.nbPalettes;
+	uint16_t const maxNbColors = options.nbColorsPerPal * options.nbPalettes;
 
 	for (;;) {
 		line.clear();
-		requireLine("GPL", file, line);
-		if (!line.length()) {
+		if (!readLine(file, line)) {
 			break;
 		}
-
-		if (line.starts_with("#") || line.starts_with("Name:") || line.starts_with("Column:")) {
+		if (line.starts_with("Name:") || line.starts_with("Columns:")) {
 			continue;
 		}
 
 		std::string::size_type n = 0;
+		skipWhitespace(line, n);
+		// Skip empty lines, or lines that contain just a comment.
+		if (line.length() == n || line[n] == '#') {
+			continue;
+		}
+
 		std::optional<Rgba> color = parseColor(line, n, nbColors + 1);
 		if (!color) {
 			return;
 		}
+		// Ignore anything following the three components
+		// (sometimes it's a comment, sometimes it's the color in CSS hex format, sometimes there's nothing...).
 
 		if (nbColors < maxNbColors) {
 			if (nbColors % options.nbColorsPerPal == 0) {
@@ -394,7 +400,7 @@ static void parseHEXFile(std::filebuf &file) {
 	// https://lospec.com/palette-list/tag/gbc
 
 	uint16_t nbColors = 0;
-	uint16_t maxNbColors = options.nbColorsPerPal * options.nbPalettes;
+	uint16_t const maxNbColors = options.nbColorsPerPal * options.nbPalettes;
 
 	for (;;) {
 		std::string line;

test/gfx/full_gpl.flags

@@ -0,0 +1 @@
+-c gpl:full_gpl.gpl

test/gfx/full_gpl.gpl

@@ -0,0 +1,36 @@
+GIMP Palette
+#Palette Name: AxulArt 32 color Palette
+#Description: 32-color palette, intended to be similar to that used in arcade and Game Boy Advance games; You can see more of my art at: https://axulart.tumblr.com/ and https://axulart.itch.io/
+#Colors: 32
+0 0 0 000000
+252 252 252 fcfcfc
+196 199 238 c4c7ee
+154 143 224 9a8fe0
+99  93  150 635d96
+41  47  101 292f65
+27  29  52  1b1d34
+255 227 174 ffe3ae
+205 187 171 cdbbab
+166 133 143 a6858f
+207 93  139 cf5d8b
+150 73  104 964968
+255 180 130 ffb482
+221 134 125 dd867d
+178 105 111 b2696f
+246 198 94  f6c65e
+228 144 87  e49057
+196 104 51  c46833
+176 208 126 b0d07e
+102 170 93  66aa5d
+82  181 171 52b5ab
+42  131 121 2a8379
+28  86  89  1c5659
+123 225 246 7be1f6
+88  159 252 589ffc
+80  105 228 5069e4
+46  68  174 2e44ae
+128 86  212 8056d4
+90  59  150 5a3b96
+255 186 225 ffbae1
+230 135 197 e687c5
+167 89  185 a759b9