engine: try to fix -Wmaybe-uninitialized that may be enabled with -Wuninitialized. Diagnostic is prone to false-positives, as compiler don't have enough data for this

engine/client/cl_scrn.c

@@ -342,7 +342,7 @@ SCR_BeginLoadingPlaque
 */
 void SCR_BeginLoadingPlaque( qboolean is_background )
 {
-	float	oldclear;
+	float	oldclear = 0;;
 	S_StopAllSounds( true );
 	cl.audio_prepped = false;			// don't play ambients
 	cl.video_prepped = false;

engine/client/console.c

@@ -1915,7 +1915,7 @@ int Con_DrawDebugLines( void )
 		if( host.realtime < con.notify[i].expire && con.notify[i].key_dest == cls.key_dest )
 		{
 			int	x, len;
-			int	fontTall;
+			int	fontTall = 0;
 
 			Con_DrawStringLen( con.notify[i].szNotify, &len, &fontTall );
 			x = refState.width - Q_max( defaultX, len ) - 10;
@@ -2238,7 +2238,7 @@ void Con_DrawVersion( void )
 {
 	// draws the current build
 	byte	*color = g_color_table[7];
-	int	i, stringLen, width = 0, charH;
+	int	i, stringLen, width = 0, charH = 0;
 	int	start, height = refState.height;
 	qboolean	draw_version = false;
 	string	curbuild;

engine/common/imagelib/img_png.c

@@ -41,7 +41,7 @@ qboolean Image_LoadPNG( const char *name, const byte *buffer, fs_offset_t filesi
 	int		ret;
 	short		p, a, b, c, pa, pb, pc;
 	byte		*buf_p, *pixbuf, *raw, *prior, *idat_buf = NULL, *uncompressed_buffer = NULL, *rowend;
-	uint	 	chunk_len, crc32, crc32_check, oldsize = 0, newsize, rowsize;
+	uint	 	chunk_len, crc32, crc32_check, oldsize = 0, newsize = 0, rowsize;
 	uint	 	uncompressed_size, pixel_size, i, y, filter_type, chunk_sign;
 	qboolean 	has_iend_chunk = false;
 	z_stream 	stream = {0};

ref_gl/gl_sprite.c

@@ -815,7 +815,7 @@ void R_DrawSpriteModel( cl_entity_t *e )
 	float		angle, dot, sr, cr;
 	float		lerp = 1.0f, ilerp, scale;
 	vec3_t		v_forward, v_right, v_up;
-	vec3_t		origin, color, color2;
+	vec3_t		origin, color, color2 = { 0.0f };
 
 	if( RI.params & RP_ENVVIEW )
 		return;

ref_soft/r_beams.c

@@ -198,7 +198,7 @@ static void R_DrawSegs( vec3_t source, vec3_t delta, float width, float scale, f
 	int	i, total_segs, segs_drawn;
 	float	div, length, fraction, factor;
 	float	flMaxWidth, vLast, vStep, brightness;
-	vec3_t	perp1, vLastNormal;
+	vec3_t	perp1, vLastNormal = { 0.0f };
 	beamseg_t	curSeg;
 	
 	if( segments < 2 ) return;