Ignore empty lines in HEX files

They are free-form enough that empty lines should probably be supported.

src/gfx/pal_spec.cpp

@@ -401,6 +401,10 @@ static void parseHEXFile(std::filebuf &file) {
 		if (!readLine(file, line)) {
 			break;
 		}
+		// Ignore empty lines.
+		if (line.length() == 0) {
+			continue;
+		}
 
 		if (line.length() != 6
 		    || line.find_first_not_of("0123456789ABCDEFabcdef"sv) != std::string::npos) {

test/gfx/empty_lines.flags

@@ -0,0 +1 @@
+-c hex:empty_lines.hex

test/gfx/empty_lines.hex

@@ -0,0 +1,7 @@
+
+5721d9
+
+a9d4fe
+
+
+ffffff