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Handle zero-byte files gracefully

--- a/src/asm/lexer.c

+++ b/src/asm/lexer.c

@@ -184,10 +184,14 @@

 	// If ftell errored or the block above wasn't executed

 	if (capacity == -1)

 		capacity = 4096;

+	// Handle 0-byte files gracefully

+	else if (capacity == 0)

+		capacity = 1;

 	while (!feof(f)) {

 		if (buf == NULL || size >= capacity) {

-			capacity *= 2;

+			if (buf)

+				capacity *= 2;

 			/* Give extra room for 2 newlines and terminator */

 			buf = realloc(buf, capacity + SAFETYMARGIN + 3);

@@ -199,7 +203,7 @@

 		char *bufpos = buf + SAFETYMARGIN + size;

 		size_t read_count = fread(bufpos, 1, capacity - size, f);

-		if (read_count == 0)

+		if (read_count == 0 && !feof(f))

 			fatalerror("%s: fread error", __func__);

 		size += read_count;

@@ -210,6 +214,12 @@

 	pBuffer->pBuffer = buf + SAFETYMARGIN;

 	pBuffer->pBuffer[size] = 0;

 	pBuffer->nBufferSize = size;

+

+	/* This is added here to make the buffer scaling above easy to express,

+	 * while taking the newline space into account

+	 * for the `yy_buffer_append`s below.

+	 */

+	capacity += 3;

 	/* Convert all line endings to LF and spaces */