fastx: improve ugly 'fgets' hack to avoid compilation warnings.

This change was already included in the previously released
version 0.0.13.2 (but I forgot to add it here).
Enables compiling with "-D_FORTIFY_SOURCE=2".

Solves github issue #1.

src/libfastx/fastx.c

@@ -321,7 +321,7 @@ int fastx_read_next_record(FASTX *pFASTX)
 		errx(1,"Internal error: pFASTX==NULL (%s:%d)", __FILE__,__LINE__);
 
 	pFASTX->input_line_number++;
-	if (fgets(pFASTX->input_sequence_id_prefix, MAX_SEQ_LINE_LENGTH, pFASTX->input) == NULL)
+	if (fgets(pFASTX->dummy_read_id_buffer, MAX_SEQ_LINE_LENGTH, pFASTX->input) == NULL)
 		return 0; //assume end-of-file, if we couldn't read the first line of the foursome
 
 	chomp(pFASTX->name);
@@ -367,7 +367,7 @@ int fastx_read_next_record(FASTX *pFASTX)
 
 	if (pFASTX->read_fastq) {
 		pFASTX->input_line_number++;
-		if (fgets(pFASTX->input_name2_prefix,  MAX_SEQ_LINE_LENGTH, pFASTX->input) == NULL) 
+		if (fgets(pFASTX->dummy_read_id2_buffer,  MAX_SEQ_LINE_LENGTH, pFASTX->input) == NULL) 
 			errx(1,"Failed to read complete record, missing 3rd line (name-2), on line %lld\n",
 				pFASTX->input_line_number);
 

src/libfastx/fastx.h

@@ -62,13 +62,23 @@ typedef enum {
 typedef struct 
 {
 	/* Record data - common for FASTA/FASTQ */
-	char    input_sequence_id_prefix[1];   //DON'T touch this - this hack will read the entire name into the variable 'name',
+	union {
+		struct {
+			char    input_sequence_id_prefix[1];   //DON'T touch this - this hack will read the entire name into the variable 'name',
 				  //leaving the prefix ('>' or '@') in 'input_sequence_id_name'.
-	char    name[MAX_SEQ_LINE_LENGTH+1];
+			char    name[MAX_SEQ_LINE_LENGTH+1];
+		};
+		char dummy_read_id_buffer[MAX_SEQ_LINE_LENGTH+2];
+	};
 	char    nucleotides[MAX_SEQ_LINE_LENGTH+1];
 	/* Record data - only for FASTQ */
-	char    input_name2_prefix[1];         //same hack as 'input_sequence_id_prefix'
-	char	name2[MAX_SEQ_LINE_LENGTH+1];
+	union {
+		struct {
+			char    input_name2_prefix[1];         //same hack as 'input_sequence_id_prefix'
+			char	name2[MAX_SEQ_LINE_LENGTH+1];
+		};
+		char dummy_read_id2_buffer[MAX_SEQ_LINE_LENGTH+2];
+	};
 	int	quality[MAX_SEQ_LINE_LENGTH+1];  //note: this is NOT ascii values, but numerical values
 					       //      numeric quality scores and ASCII quality scores
 					       //      are automatically converted to numbers (-15 to 93)